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01-01-2009, 06:30 PM   #46
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Blue,
you're right, Tokina is not the Vivitar. Not all hope is lost :-)

Abbaz,
I did try with, without and now with again, light skylight filter. Seems to be a tad better with the filter. Actually I found a lens scheme for the lens here http://www.taunusreiter.de/Cameras/Rollei_QBM_Schneider_dt.html (scroll to the bottom). Indeed the filter seems to do something.

Thanks and wishing you all a good one,
Georg (the other)


Last edited by georgweb; 01-01-2009 at 06:36 PM.
01-01-2009, 07:44 PM   #47
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QuoteOriginally posted by georgweb Quote
I did try with, without and now with again, light skylight filter. Seems to be a tad better with the filter. Actually I found a lens scheme for the lens here Die letzten westdeutschen Kleinbildcameras / Rollei QBM Mouint (scroll to the bottom). Indeed the filter seems to do something.
Georg,

Let me quote Douglas Kerr (the full article can be downloaded here):
If a flat glass plate is inserted, perpendicular to the optical axis, into the path of rays from a lens heading to form an image, its effect is to shift the point of convergence of the rays (the point at which an image is formed) away from the lens by an amount depending on the thickness of the plate and its index of refraction. In this article, we derive the expression for the amount of this shift.

In other terms, inserting a filter -- or a piece of clear galss -- into the optical path of a lens moves the focal point (the point of convergence of the image forming light rays) further away by a small but noticeable amount. The formula is:

Focal Point Shift = Thickness of the glass x (1 - 1/Refractive Index of the glass).

For a filter made of ordinary clear glass (refractive index = 1.55) with a thickness of 1mm, the focal point shift is:

1 - 1/1.55 = 0.35 mm

If the filter is located in front of the lens, the small focus shift occurs on the object plane (subject side) and can easily be neglected. If the filter is located at the rear of the lens, the focus shift occurs on the image plane (sensor/film side) and even a shift of a third of a millimeter can result in a blurry image. As a consequence, telephoto lenses designed to use rear filters are specially modified to account for the focal point shift due to the filter. Therefore, the filter should not be removed

Happy new year! Cheers!

Abbazz
01-01-2009, 08:07 PM   #48
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Shot with k20d & Tokina 500mm f8 on tripod, shake reduction off and cable release to avoid vibration. pics with crops. Mirror lenses are known for less than perfect contrast and should be used with a hood (if necessary, make one out of paper, thin foam, etc) and filter. post processing software can correct/enhance the pics. these have minimal sharpening and contrast adjustments (and no donuts). I discounted these lenses until the tokina became available. with patience and practice, you can get very good results from an inexpensive lens. dof is thin and developing good manual focus techniques is a must. these results IMO are excellent for a $90 expenditure.

Last edited by ivoire; 04-18-2009 at 09:23 AM.
01-01-2009, 08:16 PM   #49
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Heres a quick sample of the sparrow after post processing:


Last edited by ivoire; 04-18-2009 at 09:23 AM.
01-02-2009, 03:59 AM   #50
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I'm using the Tamron 500 F8, model 55B. But it's a challenge to get sharp images, you really need a tripod and as fast shuttle speed as possible. Have had some success with a monopod but consider the actual focal length of 750mm! Regarding the rear filter, was this lens supplied with a clear glass filter? I only have one ND grey filter and 3 coloured filter for black and white supplied with it. One positive effect of this mirror lens is the CA, hardly any visible at all.
Here are some pictures taken with it.

Mike.

Last edited by wavecurrent; 03-17-2011 at 02:57 AM.
01-02-2009, 04:15 AM   #51
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QuoteOriginally posted by wavecurrent Quote
I'm using the Tamron 500 F8, model 55B. But it's a challenge to get sharp images, you really need a tripod and as fast shuttle speed as possible. Have had some success with a monopod but consider the actual focal length of 750mm! Regarding the rear filter, was this lens supplied with a clear glass filter? I only have one ND grey filter and 3 coloured filter for black and white supplied with it. One positive effect of this mirror lens is the CA, hardly any visible at all.
Here are some pictures taken with it.
Mike, isn't the clear filter not already screwed into the rear? Otherwise Tamron might be able to supply a replacement, if the lens is not too old. I couldn't get one for my Tammy 300/2.8 60B, but found a current Hama filter of having the thickness riquired (luckily).

Ben
01-02-2009, 04:42 AM   #52
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ivoire,
thanks for posting very promising pics, I'll have to work on that Tokina harder :-)

And thanks everybody for hints and tips how to max out IQ, keep them coming.

Abbaz,
thank you very much for the detailed info. I've had a look at the 2 page PDF that you have linked. FWIW, my conclusions for my mirror lens would be:

If you leave the back filter off, results could be:

- Field curvature will be increased (meaning: focus at the corners will be nearer in relation to the center focus plane) BTW is there a real center on a mirror lens?

- Center focus (if there is a center) seems not to be affected

- Certain kinds of flaring could differ/increase without the filter

- Looks like it is possible to get away with NOT using the filter. I would have to do some more testing (aargh), especially corners and flaring with and without the filter. Might be worth a try also to use a very good UV-filter or polarizer on the front just to know how it works.

Thanks for the info,
Georg the techhead (not, I hope)

Last edited by georgweb; 01-02-2009 at 04:51 AM.
01-02-2009, 05:29 AM   #53
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QuoteOriginally posted by georgweb Quote
FWIW, my conclusions for my mirror lens would be:

If you leave the back filter off, results could be:

- Field curvature will be increased (meaning: focus at the corners will be nearer in relation to the center focus plane) BTW is there a real center on a mirror lens?

- Center focus (if there is a center) seems not to be affected

- Certain kinds of flaring could differ/increase without the filter

- Looks like it is possible to get away with NOT using the filter. I would have to do some more testing (aargh), especially corners and flaring with and without the filter. Might be worth a try also to use a very good UV-filter or polarizer on the front just to know how it works.
Your findings are quite valid. Especially curvatore of field will be more pronounced. Some people use the Russian Rubinar 1000/11 without the rear filter and that increases focal length slightly to about 1200mm. But this might also be due to the necessary shift of focus, as lenses experience a slight change in fl due to the focusing distance.

Ben

01-02-2009, 11:36 AM   #54
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Regarding filter for the Tamron SP 500 F8 55B lens, will a new HOYA or B+W 30.5mm UV fiter fit at the back of the lens? Found a swedish net store who sells both types!

Thanks,

Mike
01-02-2009, 11:51 AM   #55
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Here a few shots I did with K20D and Tamron 500SP a few days ago:





01-02-2009, 12:21 PM   #56
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QuoteOriginally posted by wavecurrent Quote
Regarding filter for the Tamron SP 500 F8 55B lens, will a new HOYA or B+W 30.5mm UV fiter fit at the back of the lens? Found a swedish net store who sells both types!

Thanks,

Mike
You need to know the thickness of the original filter's glass. On the old Tamron 60B (300/2.8) that was about 1mm, as I learned from the Tamron service. The Hama filter I bought for replacement had exactly the required thickness. The B+W's were too thick (2mm) and other alternatives had inferior coating, so I was happy to get the Hama HMC version.

Another point is the thickness of the filter mount. I had one other, cheaper filter with the correct diameter, but the mount was app. 1mm too stick and stuck out at the rear. I could have milled that away in the worst case, but as the Hama was a perfect match, that was not needed.

Ben
01-02-2009, 12:52 PM   #57
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Tanks for the info Ben,

I will see if I can find used ones somewhere!

Mike
01-02-2009, 02:30 PM   #58
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QuoteOriginally posted by wavecurrent Quote
Tanks for the info Ben,

I will see if I can find used ones somewhere!

Mike
That's probably the easiest option. Otherwise I have seen, that B&H still stocks some old Tamron rear filters. May be you find the correct one there. I just found the postage to Europe prohibitively expensive just for a filter...

Ben
01-04-2009, 12:31 PM   #59
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Another go-around with the Tokina 8/500. This time I really tried to do as I said in terms of how to use it.


Bokeh is not too bad, deteriorated here from unsharp mask



Contrast is getting better. Shading the lensshade with my body

That was a sunny day and I did not crop those pics too much. Tripod was still too small, must lug the fat one next time.
Georg (the other)
01-04-2009, 05:44 PM   #60
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Those are looking better Georg. If you are not using time delayed function, do so. also, using a wired or wireless remote will help. you can try shake reduction on and off and compare the results. I just put my mirrors up for sale to fund a trip to florida and 2 older lenses. hate to see them go, if the 500 or 600 doesn't sell, it will be great for birding in fl.
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