[Athanassios]

Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here.

---

Please do allow me to act like a happy child holding a huge lollypop but please do have a look at the magic of PENTAX KP along with some Adobe Camera Raw and a ... "cheap" chinese 900mm F8 lens with a hood. I am speechless!
PS: for better viewfinder magnification I ditched the Pentax 1.18x eyecap with an Aliexpress 1.50x that is even better for God shake!

All photos taken with KP @ U4/M preset mode. Only problem that KP has either 800mm or 1000 mm for "manual focal lens" while the glass is actually 880mm; hence I chose the 800mm adjustment. Also the lens may be F8 fixed but KP cannot read the aperture (T2 mount). But who cares!!!

[mlag]

For mirror lenses this are indeed good pictures...
What amazes me the most is that this 900 mm looks similar in size as my 500..600 mm mirror lenses...
(Can you share dimensions, brand? )

[Athanassios]

For mirror lenses this are indeed good pictures...
What amazes me the most is that this 900 mm looks similar in size as my 500..600 mm mirror lenses...
(Can you share dimensions, brand? )

Here you go. It’s actual mm based on a previous post here or dp according to physical dimensions is 880mm.

[Bob 256]

More info here (looks like the same lens under another name) but not in stock - too bad................with added baffles and correction lenses, someone may have come up with a reasonably good mirror lens.

amazon.com : Lightdow 900mm F8.0 Telephoto Mirror Lens + T2 Mount Adapter Ring for Canon EOS Rebel T7 T7i T6 T6i T5 T5i SL2 80D 77D 700D 70D 60D 50D 5D 6D 7D 600D 550D 200D 150D 100D 1300D 1400D 1500D : Electronics?tag=pentaxforums-20&

---

Last edited by Bob 256; 01-23-2023 at 10:27 AM.

[Athanassios]

More info here (looks like the same lens under another name) but not in stock - too bad................with added baffles and correction lenses, someone may have come up with a reasonably good mirror lens.

amazon.com : Lightdow 900mm F8.0 Telephoto Mirror Lens + T2 Mount Adapter Ring for Canon EOS Rebel T7 T7i T6 T6i T5 T5i SL2 80D 77D 700D 70D 60D 50D 5D 6D 7D 600D 550D 200D 150D 100D 1300D 1400D 1500D : Electronics?tag=pentaxforums-20&

You can find it on eBay from the same guy I bought mine. Both Lightbow and Kelda are from the same factory (I think Keldas). PS I bought the 78mm long / 105mm diameter hood separately on AliExpress for some 25$. A must.

PS2 my version is newer; it has the Pentax like grip with a “diamond shaped” handle and weights more.
900mm F8.0 Super Mirror Telephoto Lens for Canon Nikon Sony Olympus M43 Camera | eBay

[acoufap]

You can find it on eBay from the same guy I bought mine. Both Lightbow and Kelda are from the same factory (I think Keldas). PS I bought the 78mm long / 105mm diameter hood separately on AliExpress for some 25$. A must.

PS2 my version is newer; it has the Pentax like grip with a “diamond shaped” handle and weights more.
900mm F8.0 Super Mirror Telephoto Lens for Canon Nikon Sony Olympus M43 Camera | eBay

In your initial post you wrote T2 mount. But this mount isn‘t availlable on the linked Ebay site. So you got it as Pentax K-mount, don‘t you?

[GUB]

Given that the filter thread is 105mm I suspect f8 is a bit suspect. (900 / 105 = 8.6).

[mlag]

In your initial post you wrote T2 mount. But this mount isn‘t availlable on the linked Ebay site. So you got it as Pentax K-mount, don‘t you?

It’s Tmount with adapter included in delivery.
As mirrors have fixed aperture, there is no or less incentive to build lenses with lens contacts...



---------- Post added 23-01-23 at 12:14 ----------

Given that the filter thread is 105mm I suspect f8 is a bit suspect. (900 / 105 = 8.6).

With mirror lens there is always the question how much to substract for the central pancake in the front lens....

[acoufap]

It’s Tmount with adapter included in delivery.

---------- Post added 23-01-23 at 12:14 ----------



With mirror lens there is always the question how much to substract for the central pancake in the front lens....

Thanks for clarifying!

[Athanassios]

In your initial post you wrote T2 mount. But this mount isn‘t availlable on the linked Ebay site. So you got it as Pentax K-mount, don‘t you?

it comes with a Pentax K adopter for free. Likewise, the listing offers the option to get it in any other brand mount ( Canon, Nikon etc)

---------- Post added 01-23-23 at 12:48 PM ----------

Given that the filter thread is 105mm I suspect f8 is a bit suspect. (900 / 105 = 8.6).

another fellow on this forum of dp did some physics magic and had calculated that the actual mm is 880 that brinds it down to 8.38 but I cannot give an "oath". YET.... with KP's amazing SRII, ISO and sunny conditions in Greece, I am pretty much ok. After all, when I am using the 1.4x TC on my 55-300 PLM the F goes to 9 and some times KP refuses to take it "lower/faster" than F9.5. TBH this is more of an experimental toy. I just got more than I expected with alot, and I repeat a lot of Adobe Camera RAW TLC.

---------- Post added 01-23-23 at 12:55 PM ----------

Given that the filter thread is 105mm I suspect f8 is a bit suspect. (900 / 105 = 8.6).

PS* For some reason I can't explain they state that the maximum diameter is 111 (the filter thread is 105mm 100% due to the hood I put) So 880/111 = 7.92

If anyone knows and reads this maybe they can explain.

[Bob 256]

Should be easy to determine the equivalent f value by metering off a uniformly lighted wall with the mirror lens and noting the shutter speed. Switch to a regular lens and meter off the same wall using that shutter speed and see what you get for an f value. It's probably substantially higher than f8 but that should be of no major concern for this special use lens if enough light is available.

[Athanassios]

Should be easy to determine the equivalent f value by metering off a uniformly lighted wall with the mirror lens and noting the shutter speed. Switch to a regular lens and meter off the same wall using that shutter speed and see what you get for an f value. It's probably substantially higher than f8 but that should be of no major concern for this special use lens if enough light is available.

Due to its T2 and lack of electronics the camera does not read the fixed aperture and shows F— You can get focus readings since that’s another sensor but you cannot meter the light.

[Stefan Jr]

What eye eye cup you got on your KP?

Looks practical.

[Bob 256]

Due to its T2 and lack of electronics the camera does not read the fixed aperture and shows F— You can get focus readings since that’s another sensor but you cannot meter the light.

I understand that. What I was saying is that you can approximate its equivalent f number by comparing it to a lens for which you can read the f stop after shooting a known area of given brightness. This will take its central obstruction into account as well.

[swanlefitte]

. What I was saying is that you can approximate its equivalent f number by comparing it to a lens for which you can read the f stop after shooting a known area of given brightness.

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.