telephoto mirror lens，甜甜圈反射鏡，波波鏡

The optical design is based on gregory-maksutov or spot maksutov telescope, and often called as CAT ( catadioptric) lens which is a combination of mirrors and refractive lens

most of these lens are manual focus. The aperture is fixed. It is virtually free ( marketing bluff beware) of chromatic aberration, coma, and off-axis aberrations. However, due to central obstruction of secondary mirror, contrast is normally lower. However, lateral color aberration ( different image size for different colors) still exist, except on the Zeiss mirotar, which use dual corrector plates

The overall image quality depends mainly on the secondary mirror aberrations. So in lower priced models, if the secondary mirror is a separate element, it has more room for improvement.

Exposure:

The secondary mirror blocks about 1/3 of the area of the lens aperture. This in itself would result in the loss of about 2/3 stop in effective lens speed (i.e. a T-stop that was 2/3 stop slower than the f-stop). The actual T-stop would also include light losses at the reflecting surfaces and light losses (including surface reflection and bulk glass absorption) when the light passes through the refractive optical elements.

This would indicate that both the Pro Optic 500/6.3 and the Tamron 500/8 are lenses with T-stop of around 10. or 1.33 EV dimmer than f/6.3

Experience:

in modern days, user will find it difficult to use:

Manual Focus

no Image Stabilisation on lens

slow aperture

auto exposure will not work properly

with all these in one same lens, you definitely need a sturdy tripod to make a decent sharp picture, in today's DSLR standards.

conventional spot maksutov design

1000mm FL MTO and on youtube review

rubinar:

secondhand ref price usd 60 to 80 for these below:

Yashica Tomioka

Spiratone 500 f/8 Minitel and 800

Tokina

Sigma (Accura)

Vivitar

Zuiko Olympus

Minolta 250 f5.6, using mangin mirrors

recent new comers:

pro-optic

Opteka

Kelda

300mm aperture: Super-Paragon/Ohnar/Cambron

for better optics and "made in Japan" brands,secondhand ref price usd 200 to 300

Those design with "spot mirror" on the back , will have better reliability. If the secondary mirror is located on top of front meniscus glass, this mirror ( and may have also an corrector element, is cemented together with transparent optical grade adhesive ( canadian balsam ?). Over time, or due to high temperature, this adhesive may dry up or delaminate.

with mangin mirror:

canon FD reflex 500mm

Tamron SP 500mm f/8 55BB and test review

nikon nikkor 500mm f/8 new , ver C mir

secondhand ref price usd 400 ~ 600

Minolta Reflex ( or Sony )

Ttartisan 250mm f5.6 (minolta clone) review

OTOH, the price of the real Mak scopes are very competitive.

Acuter Mak 60mm focal length 750mm : ~ USD 95

Celestron C90 focal length 1250mm : USD 240 (HKD1880)

Bosma 102mm focal length 1200mm : USD 280, second hand ~ HKD1300 or lower

for Skywatcher SkyMax Maksutov telescopes:

90mm focal length 1250 mm : USD 220

102mm focal length 1300 mm : USD 265

127mm focal length 1500 mm : USD 435

180mm focal length 2700 mm : USD 1200

CCDT67 0.67x telecompressor

or celestron 0.63x focal reducer or similar

Although Celestron C6 is a Schmidt Cassegrain, not Matsutov Cass, you can a get a hang of difference from this comparison:

what is still missing is the theoretical spot diagram of these CAT lenses.

celestron knowledge base.

cajunastro review.

xitek

repair

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Scythians 斯泰基塞種西古提人

900 BC - 200 AD British museum Tomb of scythe prince, Buktarma valley, 1200 masl, Google map Herodotus 絲路上的帝國 Biblegeography 哥羅西書 3：11 在此並不分希利尼人、猶太人、受割禮的、未受割禮的、化外人、西古提人、為奴的、自主的．惟有基督是包括一切、又住在各人之內。塞種塞迦 saka 史記漢書西域傳：塞種 ctext 昔匈奴破大月氏，大月氏西君大夏，而塞王南君罽賓。塞種分散，往往為數國。自疏勒以西北，休循、捐毒之屬，皆故塞種也。匈奴列傳 Ctext ：塞王《史記》在《大宛列傳》與《匈奴列傳》中，詳細記錄了中亞至天山一帶的塞種（塞王、塞地）狀況。例如，文中記載了月氏西破走塞王，導致塞人南遷越過懸度（今帕米爾高原及克什米爾一帶） Baike Genetic history Genetics Nih griffin ? Scytho-Siberian world 塞迦 saka wiki Disappeared? Sarmatians （薩爾馬泰，奄蔡史記 , Aorsi ）and goths YouTube

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