Takumar 400/4 for Pentax 6x7
Posted 17 August 2011 - 01:45 PM
Thank you. Michal.
Posted 17 August 2011 - 09:28 PM
Posted 07 September 2011 - 04:43 PM
Posted 09 September 2011 - 12:35 PM
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.
Posted 10 September 2011 - 04:59 PM
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.
Posted 18 September 2011 - 06:25 PM
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.
Posted 23 March 2013 - 05:31 AM
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.