www.photomacrography.net :: View topic - My MPC 90mm super macro lens
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
My MPC 90mm super macro lens
Goto page Previous  1, 2
 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions
View previous topic :: View next topic  
Author Message
Lou Jost



Joined: 04 Sep 2015
Posts: 2170
Location: Ecuador

PostPosted: Sun Jan 14, 2018 5:05 am    Post subject: Reply with quote

That was discussed extensively in the linked thread, where Rik made an excellent argument, by considering the limiting cases. If the baffle is right at the sensor, it does nothing! Likewise if it is right at the aperture. The effectiveness of the baffle increases as you move away from either extreme. Somewhere near the middle (the exact spot is difficult to know) is the best balance.
_________________
Lou Jost
www.ecomingafoundation.wordpress.com
www.loujost.com
Back to top
View user's profile Send private message Visit poster's website
MarkSturtevant



Joined: 21 Nov 2015
Posts: 332

PostPosted: Sun Jan 14, 2018 11:19 am    Post subject: Reply with quote

Perhaps it is to stop the light rays before they can reflect off of something, rather than blocking them afterwards.
_________________
Mark Sturtevant
Dept. of Still Waters
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7656
Location: Near London, UK

PostPosted: Sun Jan 14, 2018 11:30 am    Post subject: Reply with quote

I've got an old pic for that too Smile



Unfortunately it can be difficult to mount baffles "in the middle", so wherever you can, would be better than nothing.

Also too as well, not all the reflections off the sides of the tubes will be "mirror", some will be diffuse, so I'd guess the more baffles the better.
_________________
Chris R
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 18794
Location: Richland, Washington State, USA

PostPosted: Sun Jan 14, 2018 12:09 pm    Post subject: Reply with quote

MarkSturtevant wrote:
Perhaps it is to stop the light rays before they can reflect off of something, rather than blocking them afterwards.

ChrisR wrote:
I'd guess the more baffles the better.

Both are true, at least up to a point. The goal is to prevent indirect paths from any point on the aperture to any point on the sensor, via reflections from the sides of bellows or tubes or whatever. Diffuse reflectors are harder to handle than mirror reflectors, because the diffuse reflector will send light all over the place after the reflection, producing a lot more paths to block.

I have seen highly detailed technical papers on optimal baffle design for telescopes, but "optimal" in that case was something like using minimal material given that you could put the baffles anywhere. With rigs like we use there are usually lots of other constraints, so optimal becomes something like getting the best baffle shape at each of those few positions where a baffle can be placed at all.

--Rik
Back to top
View user's profile Send private message Visit poster's website
MarkSturtevant



Joined: 21 Nov 2015
Posts: 332

PostPosted: Sun Jan 14, 2018 2:29 pm    Post subject: Reply with quote

I have meanwhile managed to expand the flocking with Protostar, and I put in a mock-up of a rectangular baffle sort of near the sensor. This was done before the recent bit of discussion. It is certainly true that it is hard to put up a baffle near the middle; at least I could not figure one in my case.

So here I show a longish tube of double-layered flocking material mounted near the front of the Pixco tube. It extends to pretty near the rear when the tube is fully retracted. The oily and reflective insides that are exposed when the tube is extended will be in much deeper shadow.



The mock-up rectangular baffle is shown next. It is mounted between the Pixco tube and the rear part of the Neewer ring, so it is a bit over 20mm away from the entrance to the camera. Not too close to the sensor, I hope. It is at present made of black paper. I can make a much better one once I get a feel for what size is good and avoids vignetting. Right now the rectangle matches the size of the camera sensor (~ 22mm X 15mm).


Can't really test the modifications now since the camera body is in the shop, getting its sensor cleaned. But I am excited about these additions! Very useful and profitable discussion for me here!
I am also ready to build a 2nd super macro out of other parts. This will be smaller but about as powerful. Its best feature is that it will zoom in and out a lot faster and easier because it will be built around a de-glassed telextender (that idea is very much inspired by Johan J Ingles-Le Nobel). Slow zoom is an issue with the Pixco tube since it takes many, many turns to change its length.
_________________
Mark Sturtevant
Dept. of Still Waters
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Equipment Discussions All times are GMT - 7 Hours
Goto page Previous  1, 2
Page 2 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group