Questions

[CChelle (Michelle)]

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

[Shark Bait (Stu)]

Originally Posted by CChelle

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.

1st query - This is normal in scopes of this size. You will need a much larger primary to see detail when used visually. I am not sure how big a mirror needs to be for this to take place?

2nd query - Our eyes are not sensitive enough to pick up the colour of these deep sky objects, although some do report seeing a hint of colour. This is where photography steals the show.

Astro photography:

Does your Dobsonian use a solid optical tube?

Is it close to focus with the extension tube or without?

Others have got this to work by moving the position of the primary mirror but that will limit your visual astronomy.

[Legin (Nigel)]

Nothing is going to look as detailed through the scope as any of those great images of the galaxies etc. It is all to do with the light, basically the photographs are often long exposure and usually multiple images stacked together. They also use high end gear which increases the detail captured. Specialised cameras, superior optics and focus techniques and so on.

You can see a fair bit with a 10 inch scope but the image will not look like those photographs. You would need a massive scope and some great seeing conditions.
As for photography. It depends on many things.
I currently own a 12inch Dobsonian, which severely limits my astrophotography.
Not sure if your scope is a Dobsonian or has an equatorial mount. The Dobsonian is easy to use but it doesn't have any tracking ability. Even with Goto tracking it is not possible to take long exposures.
You have to get near perfect alignment to even manage a 10 second exposure. Sure you can stack multiple exposures but field rotation then kicks in.
Field rotation means the field literally appears to rotate it is more noticeable near the edges. It gets quite severe after a few minutes. This includes if you take a ten second shot then another and another etc. Eventually the field is rotated so much that you can not stack the images.
Now you can get field derotators but they are another cost and thing to learn. Easy enough once you get it but I suspect even then other tracking errors will kick in if you are not using an equatorial mount.
But alas all is not lost. You can take great photographs of the moon Saturn, Jupiter, Mars, possibly Neptune and Uranus. You might even grab a few second exposure on a few bright deep sky objects (star clusters work well).
One relatively easy way is afocal. You just set your camera lens to infinity and point it at the eyepiece. Some people get good result doing this but I have found it to be hit and miss often with vignetting and out of focus areas. But if you take enough shots you get a few that turn out.
Attaching your DSLR is pretty easy all you do is attach the adapter and then attach it to the scope. The problem is focus. You will probably need about 45mm extra focus (plus however long the extension tube is if you have one (I have one that is only a few mm). A good thing to try is focus using an eyepiece and measure the distance to the sensor (at least close enough to it) and then see if the focus tube has that much play.
I hade lots of trouble with focus. My telescope will not focus at prime focus on my camera sensor.
I also considered eyepiece projection. Same problem with focus if not worse in some cases. However some lateral thinking got it working moderately well.
What I ended up doing is getting a camera extension tube and a Plossl eyepiece. I unscrewed the silver tube from the eyepiece and screwed that directly into the nopiece part of my adapter (it should screw off the camera adapter). Then I attached the camera extension tube via a T-ring (teleconverter). Then I attach that to my camera and telescope.
It works only with certain eyepieces,, you can not remove the end on most of them but with Plossl's I find a fair few you can. I found the best results using a 13mm and a 20mm Plossl.
Now with this method you los a lot of light. So your exposures start getting longer for example I use about 1/40th second as ISO 400 for the moon and ISO 800 for Jupiter. This is short enough to minimise most tracking errors but the higher the ISO the greater the noise you get. I usually take one or two shots and stack them. Works for me.
Keeping the extension tube as short as possible (while still allowing the eyepiece to fit inside and not inside the camera itself) will help keep exposures down.
I hope I helped you out I worked this out after a fair amount of trial and error. But now I can happily take photographs and even movies. It isn't perfect but it works.
I now have a nice CCD camera which helps with my focus issues. But alas that is another learning curve
Sorry for the long post . The photography aspect can be tricky to get right. It took me a fair bit of thinking, reading and confusion to get it right on my dob. I really like the results though . When you start capturing a few images you will be happy. The experimentation is part of the journey.

[noeyedeer (Matt)]

hi Michelle,
it's best to find a book/website that has sketches instead of images. they more closely reflect what's seen at the ep. there's also some excellent sketches on here in some of the sketching threads.

attached is a sketch from a book that reflects what I see of M42 in my 10" dob. hope it helps somewhat as to what's expected.
if all you could see was the trapezium, with little or no nebulae structure, was the moon around? best time to view any neb is certainly when the moon is new or when it's no where near the object of choice (of course you know this)

unfortunately I know nothing about photography.

matt

removed the capture as to not violate copyright .. but this may help http://www.asod.info/?p=7928 some lovely stuff on that's site

[SkyWatch (Dean)]

Originally Posted by CChelle

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

[CChelle (Michelle)]

Thank you Stu, Nigel, Matt and Dean. All of your advice is most helpful. Stu, the dob has a solid tube and focus is closer without the extension tube (adapter). Nigel, we will certainly try all of your suggestions. Dean, I didn't even know there were two more stars inthe trapezium so I will have fun now trying to find them. Ditto for the homunulus. Matt, the image link is great and has made me realise that I am actually getting great viewing. It also made me realise that I have been looking at only a small part (the trapezium part) of this object. What I see is pretty much as shown in this sketch on the same site. http://www.asod.info/?p=7671 I will have to try a much wider view. Dean, I will certainly try a deep sky filter.
Thank you all for sharing your knowledge.
Michelle

[SkyWatch (Dean)]

Hi Michelle,

Just another comment about focus for your camera: it now sounds like the camera can't get in close enough (the focal plane on the camera is set well back from the front attachment point), so perhaps you would be better trying the reverse of what I said before: remove the extension tube and hold the camera against the focuser by hand, then wind the focuser in until you achieve a focus. This will give you an idea of what sort of attachment you will need for prime focus photography.

All the best,

Dean

[barx1963 (Malcolm)]

Originally Posted by CChelle

Thank you Stu, Nigel, Matt and Dean. All of your advice is most helpful. Stu, the dob has a solid tube and focus is closer without the extension tube (adapter). Nigel, we will certainly try all of your suggestions. Dean, I didn't even know there were two more stars inthe trapezium so I will have fun now trying to find them. Ditto for the homunulus. Matt, the image link is great and has made me realise that I am actually getting great viewing. It also made me realise that I have been looking at only a small part (the trapezium part) of this object. What I see is pretty much as shown in this sketch on the same site. http://www.asod.info/?p=7671 I will have to try a much wider view. Dean, I will certainly try a deep sky filter.
Thank you all for sharing your knowledge.
Michelle

Michelle
There are actually quite a few star in the trapezium. The 4 bright stars (named A, B, C and D) are easy with a small scope while stars E and F are a little harder but can be seen with an 8" in really good conditions and are easy with a 12" so your 10" should pick them up. There are several others but very faint. I had another go last night with the 20" but failed again to see any of the really faint ones.

Cheers

Malcolm

[CChelle (Michelle)]

Thanks Malcolm. I'm waiting now for a night without heavy cloud to have a look. For some reason, as soon as I plan to view someting, we get cloud cover and even rain. I'm thinking of letting the farmers know this so they can give me credit!! lol

Dean. We have tried this but we wind the focus in as far as it will go and it's still not sharp enough. It seems to be the camera that won't focus on the mirror that's the problem. We also tried setting the camera on macro but that didn't work either. We don't want to alter the primary mirror as we've been told that will limit our viewing. We're thinking of trying next with a web cam, as soon as we get a clear night (see comment to Malcolm above).

[SkyWatch (Dean)]

Originally Posted by CChelle

Thanks Malcolm. I'm waiting now for a night without heavy cloud to have a look. For some reason, as soon as I plan to view someting, we get cloud cover and even rain. I'm thinking of letting the farmers know this so they can give me credit!! lol

Dean. We have tried this but we wind the focus in as far as it will go and it's still not sharp enough. It seems to be the camera that won't focus on the mirror that's the problem. We also tried setting the camera on macro but that didn't work either. We don't want to alter the primary mirror as we've been told that will limit our viewing. We're thinking of trying next with a web cam, as soon as we get a clear night (see comment to Malcolm above).

The camera will focus if you can get the focal plane of the mirror and the camera to coincide. Because the camera's focal plane is well back from its connection to the focuser it sounds like it needs to come in even closer. Some people use a lower profile focuser, or move the secondary closer to the primary- but that requires telescope surgery too.

Regarding the rain: the property owners in the Flinders Ranges love it when we visit: clouds love telescopes and come in for a closer look; so it nearly always rains. In July I did a public star-viewing and portable planetarium tour (my "SkyWatch" business) of Eyre Peninsula in SA. The farmers loved the rain so much they asked me to come back in September to bring top-up rain to finish off their crops....

[CChelle (Michelle)]

Originally Posted by SkyWatch

clouds love telescopes and come in for a closer look; ....

Ahah! That explains it!!!!

[OzStarGazer]

Originally Posted by CChelle

Ahah! That explains it!!!!

Indeed. The other day I went past my balcony and I saw so many stars (from inside) that I thought to take out my telescope. I took it out of the box, went on the balcony (the whole process took less than 1 minute) and I was greeted by clouds!!! (I know the telescope should be taken out 10 to 30 minutes before watching, but I didn't plan to watch. At any rate the stars had gone!)