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Does it make a difference (Canon mount)

Bigwings

By Bigwings
in Imaging - Discussion

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Bigwings

Bigwings

Posted
Posted

I am tempted to try some prime focus imaging with my SE8 SCT Alt Az

Ok I know the mount is limited but does it make any difference if I get Tmount and adaptor for 1.25 0r 2" the Revelation Diagonal has both.

Sorry if its a dumb question.

Its a Canon 1000d

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jgs001

jgs001

Posted
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It will make a difference as you advance in imaging. An Alt Az mount is exposure time limited, from about 2 minutes per frame low in the east and west, to about 30to40 seconds overhead and the North/South. The focal length doesn't affect the exposure length for this. However, the focal length will have a bearing on the tracking ability of the mount. It's much harder for the mount to track accurately at long focal lengths over the same time frame as short focal lengths. The 8SE is about 2000mm I believe (f/10) and that will tax the motors. Also being f/10 you will need to expose for longer, but you're limited in exposure time due to tracking in Alt/Az... The weight will also have a bearing on how well the drives can track over the exposure time.

When I was using a NexStar SLT with an ST80 on it, the times I've quoted I was able to achieve, but due to the drive inaccuracies, as the exposure time got up above about 60seconds, so my frame loss rate went up, till at 120s, I was losing 50% of my frames.

What you could do, mount the camera on a dovetail, use something like the 50mm and get some good widefield images.

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Carbon Brush

Carbon Brush

Posted
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Fully agree with John.

I spend quite a bit of time playing with various old lenses 28mm to 200mm, or a cheap scope (ST102) on a crude driven EQ5. Much easier than trying to get the scope to behave with a camera.

Old 42mm thread lenses are often cheap and give decent results. I use fixed (not zoom) lenses. Just costs a few quid for an M42 to Canon adapter.

Hope this is useful.

David.

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Bigwings

Bigwings

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Thanks Guys but perhaps I havnt asked my question right.

I want to use the Canon with the telescope. I already have a piggyback mount and a 70-300 zoom for the Canon.

I am looking at three possibilities.

1. Afocal with the Canon adapted to the Badder Hyperion Zoom

2. Prime focus using 1.25" adapters

3 Prime Focus using 2" adaptors as my Revelation Diagonal supports both.

Im just trying to get a feel for the best direction.

Thanks

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Nexus 6

Nexus 6

Posted
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Hi Bigwings, I have the 1000D and used on the 925 with a 1.25 t adapter and t ring, can't really comment on the other options as I have not used them.

I must say, I prefer to use the ep and have not really messed around too much with the camera on the scope, in fact i've used it more for standard everyday photography which its brilliant for. :)

Alan

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martin_h

martin_h

Posted
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As others have said, mount the camera straight to the back - there is plenty of focus travel...this is an image I took 2 years ago when I was just starting this lark...8SE and a CCD, lots of short subs and lots of time - not the best image in the world, but it was a start.:)

post-16950-133877520165_thumb.jpg

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Bigwings

Bigwings

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Thanks guys,

Kit to screw on visual back ordered from FLO.

It will be nice just to do a bit of imaging.

Mainly a visual man but you never know.....

As an aside has anyone used an SCT / Canon setup for birding?

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Demonperformer

Demonperformer

Posted
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An Alt Az mount is exposure time limited, from about 2 minutes per frame low in the east and west, to about 30to40 seconds overhead and the North/South.

Slightly off-topic, but this seems a little counter-intuitive to me.

I have been toying with the idea of getting longer exposures on my alt-az mount by selecting objects that are closer to the celestial pole (north), using the following "logic":

Because objects closer to the pole trace out smaller circles in the sky, the physical distance the scope has to move to track the object is shorter. So for an object that has a declination of 76 degrees north, although it travels the same angular distance in a given time, the scope only has to move 1/4 of the physical distance to compensate for this, compared to a star on the celestial equator. On the basis that the further the scope has to move the greater the error introduced will be, it seems to me that you should be able to extend the exposure 4x as long.

OK, your statement is based on experience, so it follows that my "logic" has a flaw in it somewhere. Can you (or someone else) point out to me where this flaw is?

Thanks.

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