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Dry fire of Pentax 6x7 + my astrocamera

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#1 Michal1

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Posted 22 September 2014 - 03:13 PM

It took me quite a long time to find out how to make the dry fire of my Pentax 6x7, i.e. to fire the camera without film inside. So this post aims to be the best guide ever to make the dry fire :) .
1) Use a battery eliminator or assure that a battery is inside. 
2) Open the camera back as much as possible.
3) Turn the small wheel in the center of frame counter with your finger so that the counter shows a number between 1 and 10. When turning the wheel, you must press it evenly, i.e. not to touch it only at one point.
dryfire.jpg

4) Close the camera door while still holding the counter dial wheel.
5) Cokc the winding lever. If you use a battery eliminator, push the safety button with it now. 
6) The camera is now ready for the dry fire!
7) When the shutter is open, you can open the camera door and look inside!
 
When I found how to make the dry fire, I learned within a few hours about my camera as much as in the previous four years that I have it. For example, I sometimes encountered the problem with mirror hangign at half way up. Now I found that this problem can have two reasons: I either accidentally pressed the MLU button when the battery was not inside, or I pressed the shutter when the battery was not inside and the safety button was not fully pressed by the battery eliminator. When the mirror hangs in the half way, it is enough to press the safety button to allow the mirror to go up.
 
Next, I found that the interior of the camera is blackened completely insufficiently (joking - partly). When you look against the light with your eye near the plane of a wall of the camera chamber, the wall is quite bright. So I made the dry fire, opened the camera's door and pasted pieces of black velour wallpaper inside. One of them hangs on the mirror at the non-reflective side. The camera is sufficiently overdimensioned so that it has no problems to lift the mirror up. I used this wallpaper to blacken the inside of my telescope, too. I hope this will help to reduce the faint light stripes that I used to have along the sides of my photos.
 
DSCF3127.JPG
 
 
And here is the overall view on my camera at its current stage. My improvements: homemade vacuum back, battery eliminator, blackened interior of the camera and MLU button taped up to prevent accidental pressing.
DSCF3131.JPG


Edited by Michal1, 22 September 2014 - 03:25 PM.


#2 SMigol

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Posted 23 September 2014 - 01:53 AM

Interesting that you have flare issues with your 67.  I've seen those bands on some color shots of mine and assumed they were from errant headlights because it didn't appear on all the frames of a certain target.  I've done quite a bit of flocking of my scope for digital work and ended up going away from it due to high temperature making the glue come off.  Instead, I've opted to extend the hood of the lens with large dew shields to reduce the effect of off-axis light.  Seems to work well and it's working for the 67, too.



#3 Michal1

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Posted 23 September 2014 - 04:54 PM

Hi Steve! The flare issues are not too serious in most cases. There is usually only very faint glow near the long sides of the frames. It is even hardly noticeable by eye on the film. But the glow sometimes becomes too aparent after stretching the photo in software. In rare cases, the stripes come out brighter. I don't know what they are. Maybe they have nothing to do with flaring. I will see whether my modification has an effect, after that I shoot more photos. This summer was cloudy and I devoted the clear nights to looking for the infinity position on my lenses.

 

The dew shields can't be used with the widefield lenses. I tried to make some to prevent dew when I didn't have the heating belts yet. The "dew shield" for the 105mm lens had to be only about 1 cm long or it extended into the field of view of the lens.



#4 SMigol

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Posted 01 October 2014 - 03:05 PM

I'll have to build a heating strap for my lenses as we're heading into winter and may experience some wet conditions.  I was able to use a large tube for flare control on both the SMC 200 and the SMC 300 lenses.  I checked visually for vignette in the viewfinder and didn't see a problem.

 

For wide fields, I'll have to make that dew strap.  Curious how your efforts with flocking turned out.

 

I've not seen much edge glow in my images, probably because I haven't stretched them very hard. 




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