Focuser of GSO 8" Newtonian can't handle the weight of my camera??

[Haggis]

I'm a beginner and I've used my GSO 8" F4 Newtonian a couple of times now. I hope I will one day succeed in making nice pictures of deep sky objects. But first I'm getting the impression that my focuser can't handle the weight of my Canon 1000D + coma corrector.

I tried to collimate the telescope as good as I can with a laser collimator. Whenever I center on a star and focus on it with an eyepiece, the star looks good. Also, when I put the star out of focus, the shadow of the secondary mirror appears to be in the middle of the out-of-focus star so I guess collimation is decent enough. Maybe not perfect, but decent. Around the edges the stars appear like little arrows pointing to the middle where they become nice and sharp again. I understand this is called coma and is normal for an F4 newtonian. Anyway, my EQ6 mount does a good job keeping stars in the middle of the image when seen through an eyepiece. However, as soon as I replace the eyepiece with my 1000D camera and look on the Live View LCD screen, the star is no longer in the center but it has moved up a bit. I have to use the joypad to center the star again and when I take a picture, the stars in the top of the image are sharp and stars on the bottom are long and arrowshaped. The bottom of the picture also has a black bar when I use photoshop and crank up the brightness (is this vignetting?)

I also have a Astro Tech coma corrector and when I connect it to my camera, the star I use to focus on is even more to the top of the image (outside of the square box in the Live View screen!) so I have to use the joypad even more to get the star in the center of the Live View screen. My guess is that the focuser can't hold the weight of the camera and with a coma corrector, the whole setup gets even heavier and causes the tube to bend a little. I'm still waiting for my 10mm spacer to achieve better focus with the coma corrector so maybe the quality of my images will improve a bit, but that won't solve the problem with the bending of the focusertube.

Can anybody recommend a good, decent focuser that's strong enough to support a 1000D camera + coma corrector? Or can I do anything to make the stock focuser stronger? Or am I doing something terribly wrong here? I've taken a look at Moonlite focusers. Many people seem to like them. But what do I need to buy to get something that will fit my GSO 8" F4 Newtonian telescope?

Thanks in advance for the help!

[Haggis]

I've taken a look at my focuser today in daylight. It doesn't look all that bad. The focuser seems to be very firm so maybe it doesn't bend after all. However, on the camera side, the whole coma corrector / T-ring assembly is a bit loose. It's so hard to express myself in english. I don't know what all the rings and adapters are called, but when I look into the bare camera body, with nothing screwed into it, I can see three cutouts where the T-ring can click into. When I attach the T-ring adapter and turn it, it gives a nice little "click" giving the impression it's all locked tight but it's still a bit loose. I can rotate the whole assembly about 1mm or 2mm's in both directions so I think that may be the issue. I'll see if I can make it all a bit more secure.

[earth titan]

I think it is the same scope that I have and the issue is not the focuser but the tube walls. I make sure the scope is rotated so the camera points up or down, so placing less leverage on the walls.

See if this helps.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[Earl]

Collimation of a f4 scope is quiet demanding a laser is not the only thing you need. There are some detailed videos on YouTube worth watching by astronomyshed

[Haggis]

Thanks for the replies! I've just received my 10mm spacer so I should be able to use my coma corrector. Now I'm waiting for clear skies. In the mean time, I'll see if I can improve my collimation skills and hopefully, next time my stars will appear rounder and sharper. I still think it's not a good thing that a star is centered in my eyepiece but somewhere between the center and the top of the image with my camera. Maybe it's the tube walls, like earth titan says. I noticed some other owners of GSO F4 8" newtons and Astro Tech F4 8" newtons (same scopes?) have reinforced their scopes with sheet metal inserts where the focuser is attached to the tube. I'll see if my next imageing sessions gives good results. If not, I may have to follow that same route. Thanks again for your help.

[jimmyjamjoejoe]

I read a thread about f4 imaging newts a while ago, and almost everyone in there said the gso and the skywatcher quatros suffered from flexing tubes, and they needed some modding to make them even remotely useful.

[jimmyjamjoejoe]

I think i remember someone using tube rings at either end of the scope, linked via dovetails to reinforce the tube a bit...

[cantharis]

I read a thread about f4 imaging newts a while ago, and almost everyone in there said the gso and the skywatcher quatros suffered from flexing tubes, and they needed some modding to make them even remotely useful.

My 8" f5 GSO has a steel tube - that certainly doesn´t flex !