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04-03-2009, 10:24 PM   #1
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800mm f8 Mirror How to's

Ok, I ordered the unbelievably cheap Rokinon 800mm Mirror lens set at f8. Is the best way to deal with this using the Aperture priority set to 8.0 then changing speed and ISO? Has anyone got experience with it?

04-04-2009, 07:22 AM   #2
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I have the 500mm f/6.3 version. It's a good lens for the cost but won't work miracles. First of all you need to learn how to focus. Difficult at first but easy once you get the hang of.

Read theses threads about mirrors:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/53490-mirror-lens-revival.html

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/39219-rokinon-...dx-mirror.html
04-04-2009, 11:09 AM   #3
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QuoteOriginally posted by fccwpe Quote
Ok, I ordered the unbelievably cheap Rokinon 800mm Mirror lens set at f8. Is the best way to deal with this using the Aperture priority set to 8.0 then changing speed and ISO?
Assuming it's a fully manual lens like most mirror lenses, Av mode will not let you set or change or even display the aperture at all - it will always shoot wide open, with F-- displaying in the viewfinder (and as with any manual lens, you'll need to enable use aperture ring in the custom menu). And assuming - again, like most mirror lenses - that it has only the one aperture and can't be stopped down or opened up - then Av mode should work completely automatically, changing shutter speed and/or ISO for you just as it would with any other lens. So if you're accustomed to using automatic exposure modes, then it actually won't be any different, except you can't actually change aperture. Or, if you're accustomed to using M mode, then just continue using that, keeping in mind you probably can't change aperture.
04-04-2009, 05:20 PM   #4
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QuoteOriginally posted by Marc Sabatella Quote
Assuming it's a fully manual lens like most mirror lenses, Av mode will not let you set or change or even display the aperture at all - it will always shoot wide open, with F-- displaying in the viewfinder (and as with any manual lens, you'll need to enable use aperture ring in the custom menu). And assuming - again, like most mirror lenses - that it has only the one aperture and can't be stopped down or opened up - then Av mode should work completely automatically, changing shutter speed and/or ISO for you just as it would with any other lens. So if you're accustomed to using automatic exposure modes, then it actually won't be any different, except you can't actually change aperture. Or, if you're accustomed to using M mode, then just continue using that, keeping in mind you probably can't change aperture.
Hi, Marc - you missed the fact that the OP is talking about a mirror lens. There is no aperture changes possible.

04-04-2009, 10:44 PM   #5
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QuoteOriginally posted by Canada_Rockies Quote
Hi, Marc - you missed the fact that the OP is talking about a mirror lens. There is no aperture changes possible.
I didn't miss it - I said, assuming it has just one aperture like most mirror lenses...
04-05-2009, 01:20 PM   #6
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Oh. Oops!
QuoteOriginally posted by Marc Sabatella Quote
I didn't miss it - I said, assuming it has just one aperture like most mirror lenses...
04-09-2009, 06:33 PM   #7
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QuoteOriginally posted by Canada_Rockies Quote
Oh. Oops!
I'm handling my beastly big M42 Rubinar 1000/10 Makpo at this very moment. (It needs about 18mm of extension rings to even clear the K20D's flash hump, so it's more like a 1200/12.) I *could* slip an aperture disc into the rear mount to stop it down further. Hmm, I could even perform surgery on some dead lens, pull the shutter mechanism, mount it behind the Rubinar, and have a one-off variable-aperture (manual) mirror! The only one on the block! Or does anyone have an M42 pancake with broken glass they'd like to donate for this Frankensteinian experiment? I didn't think so...

As for the difficult-focusing problem, this sounds like the perfect time to try focus trap aka catch-in-focus (K20D manual, p.112).
04-09-2009, 08:54 PM   #8
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QuoteOriginally posted by RioRico Quote
As for the difficult-focusing problem, this sounds like the perfect time to try focus trap aka catch-in-focus (K20D manual, p.112).
Except that CIF (or snap-in-focus as previously known) uses the AF system to determine the in focus moment, and that can result in no release with slow lenses. f/10 is pushing things a bit I think, particularly with the narrow depth of field you have with a 1000mm lens.

04-10-2009, 04:27 AM   #9
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QuoteOriginally posted by RioRico Quote
I'm handling my beastly big M42 Rubinar 1000/10 Makpo at this very moment...

As for the difficult-focusing problem, this sounds like the perfect time to try focus trap aka catch-in-focus (K20D manual, p.112).
QuoteOriginally posted by Canada_Rockies Quote
Except that CIF (or snap-in-focus as previously known) uses the AF system to determine the in focus moment, and that can result in no release with slow lenses. f/10 is pushing things a bit I think, particularly with the narrow depth of field you have with a 1000mm lens.
I wasn't thinking of my beast, so much as the OP's 600/8 or especially kristoffon's 500/6.3. But maybe if the light is bright enough... ??? I guess tomorrow I should haul out the 1000/10 and 500/8 mirrors, and the long Spiratone 400/6.3 and little Takumar 200/5.6, and see if any are capable of CIF action.

I hope the SWAT team isn't called out when I mount the 1000 and 400, they're pretty intimidating. And I don't want to scare too many tourists into running away, this town depends on them. Then I'm reminded of an old Chas Addams cartoon. A small office; reversed words on the glass door say PATENT ATTORNEY. A shabby fellow sits in front of the desk. Man in suit behind desk is standing, pointing an object out the open window, and says, "Death ray, fiddlesticks! Why, it doesn't even slow them down!"
04-10-2009, 07:57 AM   #10
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QuoteOriginally posted by RioRico Quote
As for the difficult-focusing problem, this sounds like the perfect time to try focus trap aka catch-in-focus (K20D manual, p.112).
CIF doesn't work with my rokinon f/6.3. SOMETIMES I get a blinking red dot. I pretty much doubt it'll work with f/8. It's not really aperture, and nothing to do with the actual amount of light, but the width and angle of the light cones, something these mirrors seem to be worse at than regular lenses.
04-10-2009, 09:26 AM   #11
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QuoteOriginally posted by kristoffon Quote
CIF doesn't work with my rokinon f/6.3. SOMETIMES I get a blinking red dot. I pretty much doubt it'll work with f/8. It's not really aperture, and nothing to do with the actual amount of light, but the width and angle of the light cones, something these mirrors seem to be worse at than regular lenses.
Cat lenses are known to have lower contrast than the equivalent in normal lenses. Perhaps this makes the focusing more difficult for the camera at the same f/stop. My old 400/5.6 M lens does snap-in_focus well, in good light. Come to think of it, the lens can only be used in good light
04-10-2009, 08:41 PM   #12
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Original Poster
Yes, totally true. It took me a few days, but I think I'm OK now. I live in the flight path of an Air Force base and practiced all day on the incoming planes. Hard to do, but Excellent practice!

K20D with battery grip and a big lense shooting at 45 degrees elevation gets tiring as well!

Thanks for all of your replies!!
04-25-2009, 08:12 AM   #13
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hello from france
Trap focus with an mf lens is working with pentax dslr
if you put some aluminium paper on the body contacts for the lenses ..do not forget the A contact a bit lower in the bayonnet.Features and Operation of the Ka Mount

this will activate matrix mesure, p-ttl on any k dslr pentax body and if your body is on af single position, you will be able to use av mode + trap focus and it does'nt need lot of light ...i am using the trick with a 400 F5.6 or even with a 600mm refrator f7.5 or tamron reflex 500 F8 for wildlife photo ...you need good quality glass for contrast definition ...all the rest is a peace of cake, 90% of your shots will be right in focus if your speed is fast enought.
if you need important elevation on a good tripod for planes photography consider manfrotto head 501 or 503 or an universal astrononics microstar head
have a look there:
Lunette ORION 80ED montée sur un trepied video Manfrotto + comparatif avec téléobjectifs Canon 100/400 IS L et MTO 11-CA 100/1000
enjoy
Patrick
04-30-2009, 09:13 AM   #14
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QuoteOriginally posted by BALI92 Quote
hello from france
Trap focus with an mf lens is working with pentax dslr
if you put some aluminium paper on the body contacts for the lenses ..do not forget the A contact a bit lower in the bayonnet.
Bonjour, Patrick. I am slightly confused. Should the 'aluminum paper' (metal foil) be placed over ALL the body contacts? (Ah, I should just go outside and try, yes ?!?!?)
05-04-2009, 06:00 AM   #15
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Experience with my 500mm f8 mirror lens, and help requested

I bought my USSR-made 500mm f8 mirror lens new, back in the 70s, and wanted to play around with it on a dslr. I took my lens to the local photo store to try it on a k20. The store ordered the screw-bayonet adaptor, but unknown to me the adaptor they ordered was afaik on non-Pentax type. It was thick and allowed the 500mm lens to be installed. Once I tried it out I found that the lens would not focus on infinity (because the lens was mounted too far out from the camera body). Once we figured that out the store ordered a proper Pentax thin adaptor.

Once the new adaptor was in I tried the lens on a k20 - it wouldn't fit because of the flash body overhang. Same problem on the k200. However, the lens did fit OK on the smaller K-m body, which I bought. The store was very helpful - I took an SD card with me each time so I could see the results of the lens.

When I started playing with this lens I found that my K-m would not properly expose the image. The image (sun-lit scene) was too dark (could not see it on the screen except indoors), and the histogram showed that the image was all in the left-hand quarter of the display. The only way I could get a reasonable exposure was to add +2 ev. I had thought that the camera would use its internal light meter to set the correct exposure, but that seems not to be the case. What am I doing wrong, or is my expectation wrong?

My camera settings with the 500mm lens are:
ISO 200
Av mode (by default)
Using aperture ring permitted
Input focal length set at 700mm (I had been setting it to 500mm but a Pentax rep at the local store Pentax day event said to input the effective focal length, not the physical length)
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