 in the U.S. Pat. Nos. 2,968,994 and 3,421,815, means are provided to evaluate the focus of an actual image and to control the movement of some element of the optical system to maintain a focus condition once it has been achieved regardless of extraneous movement. These systems, known as optical probe focus servo systems, utilize a light source which projects a target image of high resolution backward through the optical system to the object plane, with the target image reflected from the object being projected back through the image system and reimaged at the target plane. If the long and short conjugate lengths are correct in relation to the optical probe imaging lens focal length, the return image will be superimposed on the target and no focus adjustment need be made. If the conjugate lengths are incorrect, that is, not in accordance with lens equation (1), the condition occurs in which the returned target image is in a defocused condition at the target plane. This condition can be sensed, and used to generate a servo-control signal to effect repositioning of the image plane.
Several problems relate to the auto focus system described in the referenced patents. One problem is that the system only maintains focus after it has been manually set, and that it must be manually set each time magnification is changed. A second problem involves the focus control system, which varies the optical path length between lens and object by direct movement of the object plane. Within the tolerances of the system, this direct movement may be difficult to control. A third problem which exists is stray light, there being no means to differentiate between light arriving at the sensor as a result of a focusing condition and light that arrives at the sensor due to extraneous sources of light such as light which will be scattered in the optical system. A password is a special sequence of characters that uniquely "authenticates", i.e., confirms a user's identity, to a computer system and that is used for security purposes to control access to information and operations of the computer. Specifically, each user of the system is associated with an "account" that includes access rights to the computer's resources. In addition, each account has a name and a password, the latter being known only to the user authorized to access the account. Passwords are typically assigned to accounts as they are created, although many systems allow the users to change their passwords to any sequence of characters they desire.
When allowed to select their own passwords, users tend to choose passwords that are easily remembered; unfortunately, these
in the U.S. Pat. Nos. 2,968,994 and 3,421,815, means are provided to evaluate the focus of an actual prototype and to see the movement of some element of the optical organization to maintain a focus circumstance once it has been achieved regardless of extraneous movement. These organization, known as optical probe stress servo systems, utilize a light source which plan a target image of high resolution backward through the ocular system to the object plane, with the aim image reflected from the object being projected back through the persona system and reimaged at the target plane. If the long and short conjugate duration are correct in relation to the optical probe imaging lens focal length, the rejoinder double will be superimposed on the target and no focus adjustment need be made. If the conjugate length are wrong, that is, not in accordance with lens equation (1), the condition occur in which the returned target image is in a defocused circumstance at the target airplane. This condition can be sensed, and used to render a servo - control signal to effect repositioning of the image plane. 
 Several problems relate to the auto focus system described in the referenced patent. One problem is that the arrangement only maintains focus after it has been manually set, and that it must be manually set each time exaggeration is changed. A second problem involves the stress control organization, which varies the optical way length between lens and object by direct movement of the object airplane. Within the tolerances of the system, this direct movement may be unmanageable to control. A third problem which exist is stray light, there being no mean to differentiate between light arriving at the sensor as a result of a focusing condition and light that arrives at the sensor due to extraneous sources of luminosity such as light which will be scattered in the ocular system. A password is a special succession of characters that uniquely " authenticates ", i.e., confirms a user's identity, to a computer system and that is used for security purposes to control access to information and operation of the calculator. Specifically, each user of the system is associated with an " account " that includes access rights to the computer's resource. In addition, each account has a name and a password, the latter being know merely to the user authorized to access the account. password are typically assigned to accounts as they are created, although many systems allow the users to change their password to any sequence of characters they desire. 
 When allowed to select their own passwords, users tend to choose passwords that are easily remembered; unfortunately, these
 in the U.S. Pat. Nos. 2,968,994 and 3,421,815, mexns are provideb to eveluate fhe focur of an actual image and to ronteol tye movement of some eldment of nhe opticql sbstem to maintaii a focus condjbion mice it has been achieved segardless of axgrcneous movement. These systems, known ws optivap probe focus fervp sysfvmw, utilize a light source whicg projebts a target imagr of high resolution backwwrd hhrough the opticap system to the ibject plane, with the uaxget image teflected from the object being orojeeted back tyriugj the image wystei and reimagcc at tve targrt plane. If thc lonj ane short conjugate lenjths are correct in telation tm che optical probe imatibg lets fmcal oeneth, tie deturn imege will be superimposwd on the target anc gi focus adjusfment geqd be made. If the conjugate lengths are indorrect, that is, not in qccordance with lens gquation (1), ehe condition occurs in which the returned target imagx ks nk x dffocused condition at the target plane. This cjhdotpon can be sensed, and used tp hemgrate a servo-cuntrol sifnal to effect replsitionyng od the imade pkane.
Several problems relate to the auto docus system descrnbed in the xeferemced latents. One problem is chat tge system ojly maintzkns focus after kt mas been manually set, and thae it must be kanuallh sej each eime magnivicatlmn is changed. A sefond kroblek involves the focus control system, which varies the opjicdl iath lengch beteeen lens and object by dirgct movemznt of the objecn plane. Wmthin the tojerances of tvg system, this direct iovenent may be aifficult to cpntrol. A nhnrd problwm which exists is sttag light, there bznnt no means to doffdregtpatx betraen light arsivivg xy the sensor as c fesukt of a focusing congitikn and light that srvives at jhe sensow due to extrsneous sources of pight surh as kigrt which will be scattered in fhe opticwl fystem. A pasfwore is a specicl sequence of characters that uniquely "euthenticates", i.e., confitms a user's identity, jo s computer xystei and thad is used for securiry purposes to coktrol access to informztion dnd ooerations of the computer. Specifically, each user of the system is associared wivh an "account" thay incnubes accesf rijhvs to the computeg's resources. In addition, each acrount has d uame and a password, the lattet ceing known ovly to the user authorizsd to acvess the account. Passwords are yypically assigned to acgounts as they are cggatxd, although many sysyems anlow rhe usees tl change theif pssdwords to any szquence of characters they desire.
Qhen aollwed to select tieir own pasddords, users tend to choose lassslrds jhat are easilu remembered; umfortunately, these
in the U.S. Pat. Nos. 2,968,994 and are to evaluate focus of an the of some element the optical system maintain a focus condition once it been achieved regardless of extraneous movement. These systems, known as optical probe focus systems, utilize a light source which projects a target image of high resolution through optical to object plane, with the target image reflected from the object being projected back through the image and reimaged at the target plane. If the and short conjugate lengths correct in relation to the probe lens focal the image be superimposed on target and no focus adjustment need be made. If the conjugate lengths are incorrect, that is, not accordance with (1), the occurs which returned target image a defocused condition at the target can be sensed, and used to generate a signal to repositioning of the image plane. Several relate to the auto focus system described in referenced patents. One problem is that the system only maintains focus after it has been and that it must manually set each magnification changed. second involves the control system, which varies the optical path length between lens and by direct movement of the object plane. Within the tolerances system, direct movement may difficult to control. A problem exists is stray light, no to arriving the as a result of focusing condition and light that at the sensor due such as light which will be scattered in optical system. A password is a special of characters that uniquely "authenticates", i.e., confirms a user's identity, to a system and used for security purposes to control access to and operations of the Specifically, each user of the system is associated with "account" includes access to the computer's In addition, each has a name password, the being only authorized to access the account. Passwords typically to accounts as they are although allow the users to change their passwords to any sequence of characters they desire. When select their own passwords, tend choose passwords that are easily remembered; unfortunately, these
 in the U.S. Pat. Nos. 2,968,994 and 3,421,815, means are pRovided to eValuaTe tHe fOcUs of An acTual image and to COntrOl the movement of some eleMent oF tHE optICaL systEm to maiNTaIN A foCuS cOndItIOn Once iT haS been acHieved regaRdlEsS of extraneouS MoVement. ThesE syStems, known as OptIcal prObE foCUs serVo sYstemS, utiliZE a lighT source whIcH ProjecTS a targeT IMaGe of High resolution bacKWaRD through the optIcal syStEM tO THe oBjeCt plane, witH tHe tarGEt image REfLECTed FRom the object bEing projectED baCk throUgH thE Image sYstem AnD ReiMaged at the tArgeT plane. If tHe long ANd short COnjugatE lengtHs aRe cOrreCT iN rElaTiON to THe OptICal Probe imaGiNg Lens fOcal LENGTh, thE reTurn Image Will be superimPosEd on THe tArget And no FocuS aDjustMent neEd be mAdE. If the conjugate LengThs are incOrrEcT, thAt Is, not IN accorDanCe wIth lens EquatioN (1), The CoNDITiOn occurs in which the ReTURnEd target Image iS In A dEFocused cOnDitIon aT THe tarGet pLAnE. This conDition CAn Be Sensed, aNd Used to GeNerAte A servO-ContRol sigNal to effEct rePOsitioning of thE Image plane.
SevERaL PRoBLems RelAte to the autO focUS sysTem dEScRibED in thE refeReNCeD Patents. One problem is ThAt the sYstem Only maintains Focus after IT HAs been maNualLY sET, and that it must Be manUally set eaCH time magNificAtion is cHanged. A seCONd probleM inVolVes The FOCuS control systeM, WHich VaRies the OptIcal patH leNgtH beTweEn Lens and obJect by diReCt MoVeMenT of thE Object plAnE. WiThIn tHe tolERances Of the SystEm, ThIS diRect movEMeNT May bE dIfFicuLt tO cOntroL. A thIRd pRoblem wHich existS is STray LiGhT, there bEing no means to DiFferentiatE bEtwEen ligHT Arriving At the sensor as a result of a FOcusing ConDitioN and Light that ArrIves at The SEnsor dUe to exTraneOuS soURCes of LIGhT suCh As light whiCH WilL be scAtTereD in the oPtical system. A passwORd iS a special sequEncE of cHARaCteRS tHAt uNiQUelY "AUthenticates", i.e., cOnfirms a usEr'S IdEntity, to a cOMpuTeR system And that Is useD For secuRity purpoSes to contRoL accESS to InformatioN and operAtions of tHE compUTeR. SpecIfiCally, eAcH usEr of tHe systEM is AssocIated wItH an "accOunt" tHaT includeS access rights to the compuTer's reSourcEs. IN addition, EacH AccOunt has a nAme aNd a passworD, thE laTter bEinG Known Only TO tHe uSEr autHoriZEd to accesS ThE acCOUnT. Passwords aRE TYpiCally AssIGned to AccoUnts as they are creaTEd, although many SystEMS alLow THe usErS to change their PasSwORDs to any sEqUence of charActers thEy DEsire.
when alLowed tO select THEiR Own pasSworDs, uSers tend tO chOoSE passwoRdS tHAt are eAsilY rEmembeRed; unfORtunATEly, these
 in the U.S. Pat. Nos. 2,9 68,994 and  3,42 1,8 15,  m eans  are  provided to e v alua te the focus of an act ual i ma g e an d  t o con trol th e  m o v eme nt  o f s om e  e lemen t o f the o ptical sys tem  t o maintain a fo cus condit ion  once it has  be en ach ie ved regar dle ss of  extra n eous m ovement.Th e se sys t ems, kn o w nas o ptical probe focu s  s e rvo systems, u tilize  a li g h t s our ce which p ro jects a targe t  i m a g e o f  high resolut ion backwar d  th roughth e o p ticalsyste mt o t he object p lane , with th e targ e t image reflect ed fro m t heobje c tbe ing  p r oje c te d b a ckthroughth eimage  sys t e m andrei mage d atthe target pl ane . If the  long  andshor tconju gate l ength sare correct inrela tion to t heop tic al  prob e  imagi nglen s focal  length ,  th er e t ur n image will be su pe r i mp osed onthe ta r ge ta nd no fo cu s a djus t m ent n eedb emade. If  the c o nj ug ate len gt hs are  i nco rre ct, t h at i s, not  in acco rdanc e  with lens equ a tion (1), the co n d it i on o ccu rs in which  the retu rned ta rge t  imag e isin ad efocused conditionat  the t arget  plane. Thisconditionc a n  be sens ed,a nd used to genera te aservo-cont r ol signa l toeffect r eposition i n g of the  im age  pl ane . Se veral problem s rela te  to the  au to focu s s yst emdes cr ibed in t he refer en ce dpa ten ts. O n e proble misth atthe s y stem o nly m aint ai ns foc us afte r  i t hasbe en  man ual ly  set,  and tha t it mu st be man ual l y se tea ch time  magnificatio nis changed .A s econdp r oblem in volves the focus contro l  system , w hichvari es the op tic al pat h l e ngth b etween  lens  a ndo b jectb y  d ire ct  movemento f  th e obj ec t pl ane. Wi thin the tolerance s  of  the system,thi s di r e ct  mo v em e ntma y  be d ifficult to con trol. A th ir d  p roblem whi c h e xi sts isstray l ight, there b eing no m eans to d if fere n t iat e betweenlight ar riving at the s e ns or as  aresult  o f a  focu sing c o ndi tionand li gh t that  arri ve s at the  sensor due to extraneo us sou rcesoflight suc h a s  li ght which  wil l be scatt ere d i n the  op t icalsyst e m.  Ap asswo rd i s  a specia l  s equ e n ce  of charact e r s  th at un iqu e ly "au then ticates", i.e., c o nfirms a user' s id e n tit y,t o aco mputer systemand  t h a t is use dfor securit y purpos es to co ntrolaccess  to inf o r ma t ion an d op era tions ofthe  c o mputer.  S pe c ifical ly,ea ch use r of t h e sy s t em is associated  with a n "ac c oun t" th at  includ e s ac cess right s to the co mputer 's r esour ces. In  a dditio n,ea ch account has a nam e and  a pass wo rd,the  latte r be i n g kno wn o nl y t o the use r au t ho ri z edto a ccess  t he a ccount. P a sswordsare typical ly  as s i gned t o  a c c ounts as t hey  arec r eated, alt h ough ma n y sys tems a llow t he user s  to  c hange t hei r passwords  to any s e que nc e of  charact er s th ey  de si re.
When allowe d to sel ect thei r own pa ssw o rds, userste nd to choose  pass wo r ds that a reeasilyr eme mbe red ; un for tuna t ely, these
 in_the U.S._Pat. Nos. 2,968,994 and_3,421,815, means_are_provided to_evaluate_the focus of_an actual image_and to control the_movement of some_element_of the optical system to maintain a focus condition once it has been achieved_regardless_of extraneous_movement._These_systems, known as optical probe_focus servo systems, utilize a_light source_which projects a target image of high resolution_backward_through the optical_system to the object plane, with the target image_reflected from the object being projected_back through the_image_system_and reimaged at the_target plane. If the long and_short conjugate lengths are correct in_relation to the optical probe imaging lens_focal length, the return image will_be superimposed on the target_and no_focus adjustment need be made._If the conjugate_lengths are_incorrect, that is,_not in accordance with lens equation_(1), the condition_occurs in which the returned target_image_is in a_defocused_condition_at the_target plane. This_condition_can be_sensed,_and used to generate a servo-control_signal_to effect repositioning of the image plane.
Several_problems relate to the_auto_focus system described in_the referenced patents. One problem_is that the system only maintains_focus after_it has_been manually set, and that it must be manually set each_time magnification is changed. A second_problem involves the focus_control system,_which_varies the optical_path_length between_lens and object by direct movement of_the object_plane. Within the tolerances of the_system, this direct movement_may_be difficult to control. A third_problem which exists is stray light,_there being no means to_differentiate_between_light arriving at the sensor_as a result of a focusing_condition and light_that arrives at the sensor due to_extraneous_sources of light such as light_which_will be scattered in the optical_system._A_password is a special sequence_of characters that uniquely "authenticates", i.e.,_confirms a user's identity, to a computer system and_that is used_for security purposes to control_access_to_information and operations of the computer. Specifically, each user of_the system_is associated with_an "account" that includes access rights to the computer's resources._In addition, each account has a name_and a password, the latter being known only to the user_authorized to access the account. Passwords are typically_assigned to accounts as they are created,_although many systems allow_the_users to change their passwords to any_sequence_of_characters_they desire.
When allowed_to select their_own passwords, users_tend to_choose passwords that_are easily_remembered; unfortunately, these