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FOV possible to widen with a camera on a t mount?

clunsey73

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clunsey73

clunsey73

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I have a Celestron 6SE and a Nikon D3100 on a T adapter - both new and I am new to this too! I managed to take a few short snaps last night - but I really wanted a wider field of view - is it possible to widen the field of view in this fixed arrangement or are you stuck with what you have with the telescope? Also anyone else with the same set up and tips would be welcome - I could not get the movie mode to work on the D3100 - I assumed it was because it had no lens attached but am not sure.I have beautiful dark skies down here in Grenada and was able to clearly see M17 last night - but couldn't get the camera set up in time! (Forgot the cover inside the T adapter was still on!! = lot of frustration).

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JamesF

JamesF

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There are a couple of possibilities. GIven a fixed focal length you can't actually change the amount of sky that is covered by a given area of the camera sensor, but you can change the focal length to get more sky covered by the same area, or use a bigger sensor to record more of the image at the focal plane.

So, if your camera is APS-C, you could go to a full frame camera for instance. The problem here is that the telescope may not light the entire sensor up and you'll see vignetting on the image (quite possibly with a C6 I'd have thought). Alternatively you can get a focal reducer that reduces the effective focal length of the telescope and allows your existing sensor to cover a larger area of the sky. Reducers can be critical as regards spacing and may not produce a large enough field of view that is well-focused, so that still may not work out for you.

Or you could use a shorter focal length scope to start with. Sometimes it's easier to fix the problem at source :)

James

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VigdisVZ

VigdisVZ

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Hi

A couple of things. The 6se innately has a very "narrow" view. This is a feature of the SCT-type scopes. There are some who use a focal reducer for the 6SE but with varying success with DSLR, but it might be worth looking into.... however... The thing is: Neither the 6SE and its supplied mount (no equatorial tracking) is very well suited for long exposure AP. Don't put a load of money on upgrading it's photo capabilities as you will soon hit a wall. My recommendation is make use of what you got and pick up a copy of Steve Richards book "Making Every Photon Count" that details the best and easiest way to get into real DSO astrophotograpy.

The best entry-level wide AP scope is in my eyes a tie between the 80ED refractor and the 150PDS newton with the 80ED being the favorite.

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clunsey73

clunsey73

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Okay thanks - well I'll work with what I've got until I get familiar with it and can then scout out a focal reducer at a later date - if anyone has a celestron and uses a focal reducer you can let me know how it worked out. Cheers. I an not sure what FOV I am getting as it took me a while to get orientated and after a fantastic view of M17 tried to photograph it - but alas could not get the camera focused (turns out that if you leave the dust cap on inside of the t mount the camera can't see much of course!!) It's all a work in progress!

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VigdisVZ

VigdisVZ

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Here is a calculator I use to see what field of view I can expect from each object: http://www.12dstring.me.uk/fov.htm Just select a scope and a camera and it gives you a rough idea what to expect. Keep I mind that you need to use quite long exposures and ISO levels to get a good image, and unless you have a sturdy EQ-mount you might have a problem there. The 6SE usually comes with an alt-az mount that introduces field rotation even i it tracks the object correctly.

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JamesF

JamesF

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At the 1500mm focal length of the C6 you'll get about 2.3 minutes of arc per mm of sensor, so a standard APS-C size sensor is going to get you just under one degree along the long axis of the sensor (50 arcminutes) and about 34 arcminutes along the short side. That's consistent with me just being able to get the image of the Sun or Moon on my 450D with a 127 Mak (which has the same focal length), the Sun being about 32 arcminutes across.

James

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clunsey73

clunsey73

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Thanks for all the advice - and the link for the reducer. I know my mount isn't great for photography - well long exposure stuff anyway - but just wanted to play around and get a few images so I can record what I'm up to. I just started in this so I'm happy to spend a time getting along with what I have and then building up some links so that when I am ready to move forward I've learnt the limitations and what to expect. I guess that's why this forum is so helpful too.

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VigdisVZ

VigdisVZ

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Thanks for all the advice - and the link for the reducer. I know my mount isn't great for photography - well long exposure stuff anyway - but just wanted to play around and get a few images so I can record what I'm up to. I just started in this so I'm happy to spend a time getting along with what I have and then building up some links so that when I am ready to move forward I've learnt the limitations and what to expect. I guess that's why this forum is so helpful too.

Excellent spirit! It doesn't matter what gear you have as long as you enjoy your time using it. Looking forward to seeing your snapshots. We Nikon-users have to stick together here ;)

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clunsey73

clunsey73

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So this is the first ever photo, not very good but I`m just happy to get started - not sure what of, as I was rushing to pack up before the bad weather came in - so got 4x8s exposures off! After all the messing around all the real interesting stuff I`d been enjoying all night had moved to unobservable areas! So have no idea which stars these are but I know it was south of Antares from where I am. Just makes me keen to get out there again! but cloudy nights tonight!post-31489-0-12068400-1376007729_thumb.j

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clunsey73

clunsey73

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So the standard star prism just fits onto the back of the focal reducer without any adapters? I am just curious because the back of the focal reducer has a thread but it looks like there is no barrel for the prism to fit into - so can you somehow screw the standard prism onto the back of the reducer? Or will I need to buy an adapter of some sort too. I can't find much info on the fitting of the adapter in the celestron site so be interested to hear how you have done it.

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clunsey73

clunsey73

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PS just want to be sure - since getting things to the island is a long process! If I get the reducer then find I need other adapters that could take a long time before I am using it!!! There is no mail system as such! everything has to be imported through a broker since no one ships to - The Post Office - Grenada. And don't even think about FEDEX or DSL -once cost me 100 us dollars to send a letter via courier!

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JamesF

JamesF

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It's possible that spacers will be required. I think, but I am far from certain as I haven't tried it yet, that if you have the Celestron f/6.3 focal reducer then the distance from the back of the reducer to the camera sensor should be around 110mm. Unhelpfully the instructions don't even tell you what this distance should be. The reducer also has an SCT thread on the back, so you'd need an SCT to T-thread converter. I don't know what the length of your T-ring is or the flange-to-sensor distance for your camera, nor the depth of the thread converter, but if you know those figures then I'd assume you'd need a spacer of 110mm less the sum of those distances.

James

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clunsey73

clunsey73

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I just got a look at a good alternate thread that shows some pics. Apparently the back of the Celestron part called the visual back unscrews and the focal reducer goes where it was - and then you attach the visual back again on the back of the focal reducer. Whether I have the right spacing with this config to get the camera in focus is another matter, but at least I now know that no other bits are needed to attach the thing!

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baggywrinkle

baggywrinkle

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It does focus. If you need to use the prism that screws onto the rear thread of the focal reducer.

However if you are going to do prime focus shots then the T piece of your camera should screw onto the back of the focal reducer.

Here I am assuming that the thread on the 5SE are the same as the 6SE.

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