KP w/ " Cyclop" a 250$ (!!!) 900mm F8 catadioptric-mirror lens, from KELDA China

**Bob 256** · 01-24-2023, 11:52 AM

Originally posted by swanlefitte

I would do something similar.

The hard part is finding a large enough spot consistently lit. An 800-900mm lens at 25 meters is much smaller than for a 300mm lens. But it only needs to be part of the frame to sample after in post.
Shooting a constant lit place with a known lens at constant shutter at 3rd stop intervals and finding the photo that is equivalent in brightness is easy.
A 800mm lens at 1/x will be as bright as any mm lens at 1/x at the same f stop.

It doesn't have to be big and the shot doesn't have to be in focus so you can shoot up close with the mirror lens even though it is not in focus (actually you should have it focused at infinity). Note the shutter speed the camera dials in or what shutter speed is needed to get the correct exposure.

Switch to say a 50mm and focus at infinity. Use shutter priority and select the shutter speed from above. Now note the f-stop the camera dials in. Done. It should be close to the equivalent f value of your mirror lens.

Just an 8' x 8' wall should be way more than enough space as long as it's uniform in illumination and tone.

Last edited by Bob 256; 01-24-2023 at 11:57 AM.

Athanassios · 01-24-2023, 05:21 PM - **1 Like**

Originally posted by Stefan Jr

What eye eye cup you got on your KP?

Looks practical.

Got it from AliExpress and it comes with two eye caps, a 1.51x magnifier and viewfinder mounts for Pentax and other brands.

€ 18,43 32％ Off | 1.51X Fixed Focus Viewfinder Eyepiece Eyecup Magnifier for Canon Nikon Sony Pentax Olympus Fujifilm Samsung Sigma Minoltaz DSLR
https://a.aliexpress.com/_mrxPLTu

Andrea K · 02-28-2023, 05:16 AM

I tried, I bought it from China, 210 euro with shipment and customs... got a lemon

Athanassios · 03-01-2023, 01:01 AM

Originally posted by Andrea K

I tried, I bought it from China, 210 euro with shipment and customs... got a lemon

Sorry to hear that. I purchased mine vie eBay where you are protected against receiving lemons. I guess you ment that you received something else. If you bought it from Aliexpress the story is more hard to get your money back.

My mirror lens works fine and I also added a huge hood for extra contrast and IQ.

**Stefan Jr** · 03-05-2023, 12:02 AM

Originally posted by Athanassios

Sorry to hear that. I purchased mine vie eBay where you are protected against receiving lemons. I guess you ment that you received something else.

"Lemon" is synonym with "a bad copy".

I think that's what Andrea meant?

Andrea K · 03-13-2023, 10:48 AM

Originally posted by Stefan Jr

"Lemon" is synonym with "a bad copy".

I think that's what Andrea meant?

Yep a bad copy, these are 100% crop of some pictures:

I obtain better result using my DA* 60-250 at 250mm and cropping...

kayakfari · 2 Days Ago

This lens looks to be a re-brand or variant of the Samyang 800mm mirror also sold as Rokinon, etc..
It's very lightweight and this combined with the very short focus throw makes it difficult to get decent images hand held.
Even on a tripod, it's tough - but good enough for small size web use.

It's not really very sharp, but the close focus range makes it almost an 800mm macro.

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01-24-2023, 11:52 AM	#16
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,005	Originally posted by swanlefitte I would do something similar. The hard part is finding a large enough spot consistently lit. An 800-900mm lens at 25 meters is much smaller than for a 300mm lens. But it only needs to be part of the frame to sample after in post. Shooting a constant lit place with a known lens at constant shutter at 3rd stop intervals and finding the photo that is equivalent in brightness is easy. A 800mm lens at 1/x will be as bright as any mm lens at 1/x at the same f stop. It doesn't have to be big and the shot doesn't have to be in focus so you can shoot up close with the mirror lens even though it is not in focus (actually you should have it focused at infinity). Note the shutter speed the camera dials in or what shutter speed is needed to get the correct exposure. Switch to say a 50mm and focus at infinity. Use shutter priority and select the shutter speed from above. Now note the f-stop the camera dials in. Done. It should be close to the equivalent f value of your mirror lens. Just an 8' x 8' wall should be way more than enough space as long as it's uniform in illumination and tone. Last edited by Bob 256; 01-24-2023 at 11:57 AM.

01-24-2023, 05:21 PM - 1 Like	#17
Athanassios Senior Member Join Date: Oct 2022 Location: Glyfada, a southern suburb of Athens Photos: Gallery \| Albums Posts: 137 Original Poster	Originally posted by Stefan Jr What eye eye cup you got on your KP? Looks practical. Got it from AliExpress and it comes with two eye caps, a 1.51x magnifier and viewfinder mounts for Pentax and other brands. € 18,43 32％ Off \| 1.51X Fixed Focus Viewfinder Eyepiece Eyecup Magnifier for Canon Nikon Sony Pentax Olympus Fujifilm Samsung Sigma Minoltaz DSLR https://a.aliexpress.com/_mrxPLTu

02-28-2023, 05:16 AM	#18
Andrea K Pentaxian Join Date: Mar 2009 Location: Rome, Italy Posts: 800	I tried, I bought it from China, 210 euro with shipment and customs... got a lemon

03-01-2023, 01:01 AM	#19
Athanassios Senior Member Join Date: Oct 2022 Location: Glyfada, a southern suburb of Athens Photos: Gallery \| Albums Posts: 137 Original Poster	Originally posted by Andrea K I tried, I bought it from China, 210 euro with shipment and customs... got a lemon Sorry to hear that. I purchased mine vie eBay where you are protected against receiving lemons. I guess you ment that you received something else. If you bought it from Aliexpress the story is more hard to get your money back. My mirror lens works fine and I also added a huge hood for extra contrast and IQ.

03-05-2023, 12:02 AM	#20
Stefan Jr Site Supporter Join Date: Jan 2015 Posts: 269	Originally posted by Athanassios Sorry to hear that. I purchased mine vie eBay where you are protected against receiving lemons. I guess you ment that you received something else. "Lemon" is synonym with "a bad copy". I think that's what Andrea meant?

03-13-2023, 10:48 AM	#21
Andrea K Pentaxian Join Date: Mar 2009 Location: Rome, Italy Posts: 800	Originally posted by Stefan Jr "Lemon" is synonym with "a bad copy". I think that's what Andrea meant? Yep a bad copy, these are 100% crop of some pictures: I obtain better result using my DA* 60-250 at 250mm and cropping...

2 Days Ago	#22
kayakfari Senior Member Join Date: Oct 2016 Location: South Florida Posts: 169	This lens looks to be a re-brand or variant of the Samyang 800mm mirror also sold as Rokinon, etc.. It's very lightweight and this combined with the very short focus throw makes it difficult to get decent images hand held. Even on a tripod, it's tough - but good enough for small size web use. It's not really very sharp, but the close focus range makes it almost an 800mm macro.

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