Focusing

[MICKYJD65]

Has anyone got any tips on how I can focus the stars better than I can now? At my age my eyesights not so good anymore haha. Problem I find is that when I try to focus through the camera it's a case of hit and miss which is frustrating me. I am using a canon 350d on a Celestron 8" scope. I have read about something that you can place on the front of the scope but can't remember what it's called or where I could get one. 

[JamesF]

I think you mean a Bahtinov mask.  FLO sell them, as do many others, but you can even make one yourself to try out.  Just remember to take it off the end of the OTA once you have finished focusing :)  DAMHIKIJKOK [1]

James

[1] Don't ask me how I know.  I just know.  OK?

[discardedastro]

So many hours of light when imaging lost to forgotten Bahtinovs... ?

They're a great way to achieve good focus though, especially with a DSLR setup. The other approach, with or without a motorised focuser, is to use software to measure focus quality (based on FHWM or HFR) and just do a binary search by hand. This takes a lot of patience though and can be infuriating.

[AstroAdam]

Yup - a definitely second on the Bahtinov mask.  It makes so much difference.  Either that or an auto-focuser, which can wither be bought or self-built, but costs more and is more difficult to set up and run.    I'd stick with the mask - you can pick a decent one up (star sharp masks are great) for about £15-20 I think...   Or you can make your own one of those too... the following link is a bahtinov mask generator that you can use to make one out of thin foam or similar yourself....

http://astrojargon.net/maskgen.aspx

[Danny83uk]

Bahtinov mask from FLO

Guide to using one

Use you camera in live view if you have the screen. You can then zoom in and get a good accurate look at whats looking like.

 

[knobby]

If you want to try something quick and easy to make before you buy a Batinov, try a DIY 'Y mask' similar to a Batinov but far easier to make.

[Luna-tic]

I found that the DSLR's screen is just too small for me to see well, even with a Bahtinov mask, I can't see the diffraction lines well enough to determine a good focus. (I'm also getting older) I bought an accessory  7" screen that plugs in the HDMI port on my DSLR. It has a hot shoe mount that allows attachment to the camera, although that doesn't work well for telescope balance, and also comes with a gizmo that allows strapping the screen to a light bar (made for professional photographers). It works well clamped to a tripod leg. The screen has quite a few functions that work well for AP. The one I like is a focus function, it puts a fine red line around the screen subject when it is in focus. The screen will show anything bright enough to be seen in the camera's screen, it is a 1920x1200 pixel resolution. The screen is battery operated, has its own battery on back that removes for recharging, and it will last long enough for a good imaging or viewing session at night. I sometimes use it at outreach sessions by installing the camera on an EP (or use it prime focus) and viewers can see the image on the screen rather than having to squint into the EP. Works great for young kids who want to grab the scope. The screen backlight can be changed to several colors, including a red screen, and has a light shield that helps block any glare for other observers. The screen is fairly bright, so I usually hang a small dishrag over the screen shield so it doesn't ruin my or others' night vision.

 

[MICKYJD65]

Hi all thanks for the info on this I'm pretty sure my camera doesn't have live view  on it and the Elvid fieldvision is a bit pricey for me at the minute. So the Bahnitov mask looks like the way to go for now.  Thanks for the links I've already downloaded the template so will let you know how it goes.