Thread: Questions
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Old 26-12-2013, 12:32 PM
SkyWatch (Dean)
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Join Date: Jan 2013
Location: Adelaide
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Quote:
Originally Posted by CChelle View Post
Hi. I have had my scope (an Orion 10" dob) for 18 months now and have had many nights of great fun with it. I have also purchased a set of Orion eyepieces and coloured filters and have enjoyed them. However, I have some queries that I have not been able to discover the answer to by myself.
Firstly, I can see many of the spiral galaxies through my scope, but they only look like disks and no spiral details are seen. Is this because a 10" scope is not big enough to bring out these arm details?

Second, I have had what I think are great views of the Orion and Carina nebulas. I can clearly see the four baby stars in Orion and the Carina star in Carina, but my views look totally different to the (black and white) photographs I see in books. The photographs are far, far more detailed. Is this normal? I do not use any filter for looking at nebs. Would a filter make a huge difference?

Unfortunately I cannot photograph what I am viewing and that brings me to my third question... I have a digital SLR and I have purchased the extansion tube to go between my camera and the eyepiece fitting on my scope, but I cannot get the scope to focus sharply when the camera is attached.

I hope some of you can help with these queries.

Thanks in anticipation

Michelle

Hi Michelle,

We are really spoilt nowadays with the amazing images people are getting, so it is often a surprise when we use a scope because we expect much more detail. However, just a couple of comments:

- you won't see much detail in spiral galaxies in a 10" scope, but you can improve your chances by making sure you are fully dark-adapted and there are no lights around you. Using averted vision helps too: looking very slightly to the side of the object and training yourself to notice more detail (take your time: you will see more and more as you spend time on the object.) Some spirals are easier than others to practice on: try NGC 1365 in Fornax for instance: a lovely barred spiral.

- try looking for things that are very hard to photograph, eg: like the 5th and 6th stars in the "trapezium" in the Orion nebula. Finding objects like that can be very satisfying, and helps to train your eye! Zoom in on Eta Carina and see if you can notice detail in the "homunculus" nebula around the star: like tiny cabbages either side. I have seen these in a 4" scope, so a 10" is capable of some nice detail at high power on a good night.

- quality nebula filters will help with emission nebulae. I use a "deep sky" (broad band) filter and it effectively adds a few inches to the scope's aperture in terms of the apparent brightness of the image. The views of the Orion nebula and Eta Carina for instance are improved enormously: and become comparable to some of the photos. I find this filter is better for me than the narrow-band filters like the OIII because it allows more star-light through, and the image seems more natural. However, an OIII does give amazing views of nebulosity. Well worth borrowing some to check them out. Unfortunately filters don't add much to viewing galaxies.

- regarding the focus problem: it sounds like the extension may be the wrong length so you can't reach that elusive focus point. Try moving the extension out a bit by hand with the camera attached and see if focus improves so you can estimate how long you will need.

- check out some of Sue French's articles in S&T: she offers a lot of good advice for visual work.

All the best!!!

- Dean
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