topic Re: Brightening the image on the viewfinder in EOS DSLR & Mirrorless Cameras

Brightening the image on the viewfinder

picturescue — Fri, 09 Jan 2015 21:45:00 GMT

Is there anyway to brighten the image on the viewfinder? I've only used my camera once so far for astrophotography and I noticed the image was very dim on my viewfinder. So dim that I had to guess when I had the image on my sensor.

Thanks

Re: Brightening the image on the viewfinder

cicopo — Fri, 09 Jan 2015 21:50:59 GMT

You're looking thru the lens & the only way I know of to see a brighter image is with a faster lens. What is the max f stop of the lens you are using & is it a zoom that's zoomed out to a smaller f stop?

Re: Brightening the image on the viewfinder

picturescue — Fri, 09 Jan 2015 21:54:29 GMT

Because I bought this camera for astrophotography purposes only, I didn't buy a lense. I only bought the camera body. I use my telescope for the lense and it has a focal ration of f/5

Re: Brightening the image on the viewfinder

cicopo — Sat, 10 Jan 2015 01:04:43 GMT

That seems like a "bright" telescope. How large of a diameter is it? We have at least 2 members who are very knowledgable about astro photography but they may not associate your question as posted to using a telescope so it might be a good idea to re post & mention what you're doing in the title.

Re: Brightening the image on the viewfinder

TCampbell — Sat, 10 Jan 2015 02:49:39 GMT

Ahh... yes the stars are indeed VERY dim. You wont be able to see to focus them.

It turns out that in space, if ANYTHING is in accurate focus, then EVERYTHING is in accurate focus. That means you can focus on a bright star (for example) and then move to a fainter & more difficult to see object and still be sure that the telescope is focused (tip: use your focus lock screw on the telescope after you've achieved accurate focus.)

You have a few options to focus, but I'll just mention two of them.

#1 - Point the telescope to a moderately bright star. Switch the camera to "Live view" mode, then use the live view zoom function to increase to 10x zoom. Adjust focus to get the star down to a pinpoint. Lock the focus screw on your focuser, then move the telescope back to the object you'd like to photograph and begin capturing your images.

While this sounds easy enough... atmospheric "seeing" conditions can actually make it somewhat difficult to be sure when you really are focused as well as possible. So there is a better method (and this is the method I use).

#2 - Buy or make something called a "Bahtinov focusing mask". The focusing mask goes over the front of your scope (like a cap) but it has slots cut into it in a specific pattern. These spots cause stars (moderate to bright) to throw diffraction spikes. You'll see three spikes. Two in an "X" shape and a third vertical "|" through the middle. As you adjust focus, the middle spike will move across the "X". When the vertical spike is centered in the intersection of the "X" you have achieved perfect focus. You can remove the mask, point to the object of your choice, and begin imaging.

You can find instructions to make your own at astrojargon.net (see: http://astrojargon.net/MaskGen.aspx ) If you make your own, the site has a generator (it'll ask you to enter some parameters about your scope and then generate a template which you print out and cut (trace it onto a thicker material).

I purchased my masks. Numerous vendors sell these. Such as: http://spike-a.com or http://www.kendrickastro.com/kwikfocus.html or http://www.farpointastro.com/bmask/bmask.php

I didn't think I had one of these images on my computer (I usually delete them when I'm done focusing) but here's a photo taken with the focusing mask on the scope. If you inspect that brightest star near the middle you'll see those diffraction spikes. Becaue the long center spike is exactly centered in the two outer spikes that form an "X" it measn this scope is now perfectly focused. The scope can now be pointed at any other object in the night sky and begin imaging.

BTW, if you look very closely, you'll see that every star actually throws the diffraction spikes, but they're not very big unless the scope is pointed at a moderately bright star.

Re: Brightening the image on the viewfinder

picturescue — Sat, 10 Jan 2015 10:48:20 GMT

My scope is 130mm. I got into this hobby 2 years ago. I've actually been taking my time learning about it so I don't screw up and spend alot of money on something I won't ever use. My first scope was actually a 70mm refractor which I don't even use anymore but it helped me learn alot and has brought me to where I am today.

Re: Brightening the image on the viewfinder

RobertTheFat — Sat, 10 Jan 2015 21:28:17 GMT

@picturescue wrote:
My scope is 130mm. I got into this hobby 2 years ago. I've actually been taking my time learning about it so I don't screw up and spend alot of money on something I won't ever use. My first scope was actually a 70mm refractor which I don't even use anymore but it helped me learn alot and has brought me to where I am today.

There's a nomenclature issue that you might need to keep in mind when conversing in this forum. When we photographers mention, say, a 100mm lens, we're referring to the lens's focal length. When an astronomer talks about a 70mm refractor, I'm pretty sure he's referring to the diameter of the front element. At least that's how it was when my brother (who was into astronomy) and I (who was into photography) were kids. I presume it's still the case.