• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Stopping down with modified diaphragm (1 Viewer)

Hi Tom, you input is most welcome of course :)

The second sample I showed on my post above has the baffle at roughly 80%, but still the drop on light is very noticeable, so is vignetting. The place I don't have vignetting at all, is close to where I put the baffle on the first sample, at 65% more or less.

I wish I could get by with a 25mm aperture, but I really can't see it working in my scope... I don't know why this diference between my scope and Paul's, and now yours too.
 
Thanks for the info Tom.

Can't seem to see your photos though.

Ideally they need to be about 800 pixels wide, no bigger than 1024 wide, either way 395k max file size. Scroll below the message window and click on the 'Manage attachments' button to upload them.

Paul.
 
Paul Corfield said:
I presumed they were spot welded in place as mine have never moved and I've certainly pushed stuff up against them, sometimes quite hard. I had a look just now and they do indeed move but they are a very tight fit, in my scope anyway. I can see though that their position could vary from scope to scope at the manufacturing process.

With your new focuser I guess you wont have any in the scope anyway?

Paul.
Click to expand...


The first time i decided to flock the tube, one of the 2 tube baffles kind of fell out. I guess i nudged it, but if that was spot welded in, i'm a banana.
The 2nd one i just took out to see what difference it made to IQ, another un-spot welded baffle. It didnt really make any difference. I suppose because there's plenty of baffling elewhere

I'm not sure what you mean about not having any baffles with the new focuser Paul ?
 
I didnt realise there were any baffles inside the old focuser - or indeed the new one

Just had a look at the old focuser, and presumably, those 2 rings ( barely a few mm across ) are so small that i didnt think they were baffles. The diameter must be nearly the width of the focuser tube itself. They must be letting in about 99% :eat:

EDIT

No baffles at all in the new focuser tube
 
Last edited:
The baffles in the focuser are the ones we have been discussing regarding to how they compare to the size of the diaphragm.

I certainly wouldn't take out the ones in the main tube. I kept them in and flocked them as well as the inside of the tube. Baffles inside the OTA are quite an exact science. There's ways to calculate where they should go and what size the hole should be etc.

Paul.
 
I can still see the marks where they were mounted and should have been spot welded. But since there's little difference in results, i dont feel the need to bother refitting the scope tube baffles. Especially since there's so much baffling in other areas already.
 
Actually Paul, I was talking about the one's on the main tube. Those could easily be out of place and masking your aperture.

When you say "2/3 the way up" for the iris location, you mean 2/3 for the lens side or for the other end? I assumed for the lens side.
 
About 1/2 way to 2/3 up the focuser tube is where I'm putting the diaphragm blades.

For the original baffles, you can measure the hole diameter and use that figure to calculate exactly where it should go based on the scopes focal length.

Example here.

Paul.
 
Yes, that's the way I used to measure my baffles, and confirm it later with photos to notice the difference in exposure. The rear baffle was definitely too up front.
 
I've been reading this thread with some interest because one of the few things holding me back from buying an "astro" scope has been the (seemingly) inability to "stop down" to gain some depth-of-field. However, I think I may have found a solution from one of the USA's esteemed optical supply houses, Edmund's Precision Optics. They have a T-Mount Iris Diaphragm assembly (http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=1966) which looks like it may do the trick and without doing too much cobbling together of other parts. What do you folks think?

Chris
 
Musoman,,Re your question, "Wouldnt it mean cutting a slot in the focus tube to allow the aperture lever to poke through ?"... I have done this to my scope, cutting a slot in the top of a 2" extension tube, and it works very well (see my post of 31st August, but still am unable to be able to post an attached photo of it as paper clip icon does not respond nor do I see an `attachment button`)The position of the diaphragm I have found to be from 75% to 80 % of stated f.l. of objective, but I am sure that this ideal distance would actually change in measured distance according to whether you use scope for say object at 20 metres or at infinity. And actual max. opening size should be a couple of mm. larger than next lens in the scope, i.e. field lens of eyepiece or barlow lens
 
Chris B.No need to spend 99 dollars, one from an old bellows camera will do the trick...around 20mm max. dia. opening. Just extend the operating lever by soldering on a small brass extension.Tom
 
Paul, you mean the iris should be place within the focuser tube, the one with the rack? And it moves when focusing?

tjd, have you been posting with quick reply? If you want to attach something, go to "Go Advanced" (just below the quick reply box) and everything are there. Do note that you have to size down your file or else it will be rejected. Do include pics of your setup and sample shots.
 
alphan said:
Paul, you mean the iris should be place within the focuser tube, the one with the rack? And it moves when focusing?
Click to expand...

Yes, I found the best place to avoid any vignetting was to have it inside the focuser tube. Mine is mounted on the end of my extension tube so all I do is pull out the extension tube from the scope, adjust the aperture and put the extension tube back in the scope. To give an idea how far up the focuser it is, my diaphragm blades are around 4.5" from the end of the extension tube. When it's on the scope I'd say it's about 5.5" up the focuser. This is why the Edmund Optics T-mount one wouldn't be any good, it would be too close to the camera.

Paul.
 
Paul have you got a photo of your focus tube with diaphragm fitted ?

I'm struggling to see how this works
 
Paul Corfield said:
Yes, I found the best place to avoid any vignetting was to have it inside the focuser tube. Mine is mounted on the end of my extension tube so all I do is pull out the extension tube from the scope, adjust the aperture and put the extension tube back in the scope. To give an idea how far up the focuser it is, my diaphragm blades are around 4.5" from the end of the extension tube. When it's on the scope I'd say it's about 5.5" up the focuser. This is why the Edmund Optics T-mount one wouldn't be any good, it would be too close to the camera.

Paul.
Click to expand...

Good one Paul. For a while I thought the Edmund diaphragm would be nice and be followed, but you seems to proof it otherwise. If that is the case, we should work on having no light loss iris size to avoid having to take out and adjust or remove iris. I suppose the ideal iris position would also vary with focusing.
 
Warning! This thread is more than 14 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Similar threads

has530
SVBONY SA205 Review
Replies
3
Views
633
has530
has530
james holdsworth
Stopping down a binocular
Replies
12
Views
1K
Bino Steve
B
G
Kowa TSN-773's and 774's with the TE-11WZ 25-60x Wide Eyepiece on Sale for only $1,899.00
Replies
0
Views
941
gr8fuldoug
G
D
Sky Rover Banner Cloud 8x42 APO Review
2
Replies
29
Views
4K
dries1
dries1
P
Vortex Razor HD 13-39 x 56 - first impressions
Replies
8
Views
4K
Steve Babbs
Steve Babbs

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)
Back
Top