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Takumar 400/4 for Pentax 6x7

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#1 Michal1

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Posted 17 August 2011 - 01:45 PM

I get an bargain offer to buy this lens. Is it good for astrophoto? Have you ever seen a photo of the sky taken with it?
Thank you. Michal.

#2 Nebhunter

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Posted 17 August 2011 - 09:28 PM

Michal I'm trying to search my memory to find some astro images with it, but not much comes to mind. Shooting it a f/5.6 should make it a fine lens going by what I've read.

#3 Michal1

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Posted 07 September 2011 - 04:43 PM

The lens is still not in my possession, but its owner kindly let me to test it before buying. The testing frames are being developed now but I have some findings already. When I saw it for the first time I was surprised by its enormity. I was surprised even more when I took it into hand. It can be held in two fingers only. It has, in contrary to my other lenses, the outer bayonet. After reading of this instructions and a bit of training I was able to attach the lens to the camera body in darkness with my red torch only. The lens has its tripod mount with different distance of holes than the camera body. I had no choice but to attach the camera by the body. Therefore the load on my lxd-75 mount was highly unbalanced and there was a great lever on my carrying frame which was originaly designed for my 35mm Praktica. I was photographing near the zenith to minimize the twisting. If I decide to buy the lens I will have to make an attachment for the lens mount. I could see the lens performance only on the focusing screen with the help of a magnifying glass. Certain amount of vignetting is noticeable at f/4. The chromatic abberation at high contrast edges is also visible at this speed. I will upload the test photos when I get them.

M.

#4 Nebhunter

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Posted 09 September 2011 - 12:35 PM

The outer bayonet takes some practise to figure out. The 400EDIF thankfully uses the inner, but on the Tec 140 it's the outer and can be difficult.

I can see where vignette may be a bit on an issue at f/5.6 but you can fix that. Some CA will be visible but that should be about the same as all the other f/4 Takumar lenses and is manageable with some help from the software. I don't think you could expect much more without going to an EDIF lens.

To minimize CA I would think critical focus would be necessary. Jim just did a test with his 200 Tak lens, and I'm sure he was surprised by how far off the stop he was to get critical focus. You may want to ask Jim about his test.

Once you get to f/8 - for daytime shooting the Tak lens will pretty much match the results from the EDIF lens, but that does little for astro work.

You have to admit, and handling a large lens like the 400 is neat experience. A solid mounting would be critical to any good astro shots. Enjoy.

igor

#5 Michal1

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Posted 10 September 2011 - 04:59 PM

I have the developed film already but not scans. As I expected, the images are blurred by motion significantly. Vignetting is not noticeable at f/5.6. Chromatic aberration is worse than that of my other Takumar lenses. White stars have one-sided purple haloes. The aberration looks acceptably when I look the frames with a magnifying glass only. The truth will come out after scanning.
I've done only one astronomical photo at f/4 on the Fomapan 100 film. As I've said in another thread, that film suffers hardly of recprocity failure. On a 30 min photo of M 31, there is only its core and several bright stars in motion so that it is worthless. At f/4, I have one daylight photo. I can't find a trace of vignetting on it.

#6 Michal1

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Posted 18 September 2011 - 06:25 PM

Here are the test photos along with short descriptions
http://www.astro.cz/.../Takumar 400mm/
A photo by 200mm Takumar is added for a comparison.
Some of the photos are almost 24Mpix!!!
My setup will have to be upgraded to work with this lens.
If you have questions on the 400mm lens, please ask.

#7 Michal1

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Posted 23 March 2013 - 05:31 AM

You could already see some of my shots with this lens. Now I offer to see their original unprocessed versions:
http://www.astro.cz/.../Takumar 400mm/
They are those labeled as "original". They were only downsized to 50% and converted to jpg. The processed images can be found here. The NGC 7000 image is the eastern part of a two plane mosaic. You can download a cut-out of it in the 4000 dpi resolution and 48 bit depth here. The instructions for download are at the end of this post. And you can see it in the jpg format after short processing in the full 4000 dpi resoultion here.

I've tested the lens only wide open at f/4 and at f/5.6.

The images taken at f/4 suffer of vignetting a lot. It can be partially reduced by Photoshop's lens correction filter, but the traces of vignetting are still apparent in the colour of background. The images are soft and the bright stars come out very big. I don't recommend to use this lens at f/4 in most cases.

The situation becomes better at f/5.6. The vignetting is reasonable and it is well reducible by Photoshop. The colour aberration is still evident. The abberation is more pronounced for bright stars. The fainter stars seem to be much less affected by it. The best way to reduce the aberration I found is to select the blue and red fringes of the stars in Photoshop and decrease their saturation.






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