View Full Version here: : Question for experienced observers
Been getting into astrophotography so much lately I’ve almost forgotten what it’s like to look up and gaze at the jewels. I sold all my old scopes which were great for visual, for new ones which are better for astrophotography. But with my RC8 (8” f/8) last night I still managed to see quite a bit (I could just make out the arms in M83, very slight variations in the dust lane of Centaurus A, the dust lane in Sombrero and faint detail on the keyhole in Carina nebula.) and found 100x to be a good magnification to sit on.
So my question is this – Is there any real difference between using, say, a 13mm with a 10” or a 16mm with a 12”? If anything the 13mm should increase contrast. I am asking because the price difference between the 10” and 12” is almost $1000 (Long story, but that is what it comes to). For that much money I could get a Ethos and Delos EP!
So what are your views? And with those sized dobs, what magnification do you IIS guys commonly find yourselves viewing at for DSOs?
28-06-2012, 11:33 PM
Are you talking about a 10" dob versus a 12" dob? If so I would be very surprised if there is a $1000 difference! At Bintel at the moment the price diff on the full goto dobs is only $500.
Perhaps be more specific on the scopes and specific EPs you are asking about.
I probably should explain hey! I’m getting a good deal on a used 10” skywatcher dob. After using push-to for many years, and now using Goto on my NEQ6, it’s very hard to go back! So I was going to get the skywatcher goto upgrade kit for the dob. It’ll come to around ~$1100. Compared to a brand new 12” Goto, it’s about a ~$1000 difference.
I guess it’s not so much about the EPs as it was theory – Assuming the same quality eyepiece (Lets say a Televue Delos) would it be worth getting the 12” and using a 17mm or a 10” and a 13mm? Because for $1000 I’m not sure if the difference from a moderately light-polluted backyard would be worth it. Plus 13mm would yield better contrast from the sky on DSOs.
Hence me coming to this part of the forum :) I was hoping perhaps you or anyone else could give me your advice on the difference it would make!
29-06-2012, 08:32 AM
Malcolm's pretty correct, there's a difference between 10" and 12" scopes, but it's not huge. It comes down to what you can handle physically and financially. If you can manage a 12" then go for it. A 10" will fit on the back seat of most cars and will give you years of good service.
Magnification really depends on the size of object and the seeing. A large extended area such as Eta Carina requires a wide field, then more power for a closer look. My eyepieces are all Naglers, 22, 17, 12, 9, 7, 5. I normally use the 12mm Nagler first for most DSO's (125X in my 12") and the 7 or 9mm Nagler (214X and 167X) for most small galaxies. For planetary nebulae (especially the small ones) I use whatever the seeing will permit. My shortest EP is the 5mm Nagler (300X). Quite often the seeing doesn't permit it's use very often, but when it does, then it's worth it. Some good quality filters (UHC and O-III) are swapped around when examining nebulae (gaseous and planetary) to see what works best.
Thanks for the info. I am leaning towards a 10”, I don’t think I can sufficiently justify the extra money (and weight) for the difference in views. To be honest I was very happy with my old 8” newt and now spend most of my time imaging now so not looking for anything major.
As for the magnification, I see there’s a new post related to it, but yea of course it depends on the size of the object. I’m not too concerned about the larger objects as they tend to be brighter and easier to see details. So essentially you use 120x and ~200x depending on your target? I think that would be reasonable for me to start on, getting two EPs to give that range. I noticed you have the 22T4, how does it perform? I was thinking a 22T4 and then an Ethos 13mm. Have you looked through a delos or ethos? Reckon its worth extra $$$ or trading for a lower AFOV?
By the sounds of it, for the same magnification there won’t be too much a difference between the 10” and 12”. I’ll get the filters much later down the track, having a hard enough time decided with dob to get! Thanks Paul
29-06-2012, 01:03 PM
The 22T4 is great for extended objects or just scanning around, excellent sharpness and contrast. I haven't felt the need for the Nagler 26 or 31 as the 22 Nagler's wide field is just right for my needs. The range I have picked could easily be different, maybe substituting Pentaxes at the shorter end or Vixen LVW's but I'm happy with what I have. They cover all the DSO's I am looking for. Weight is a consideration also. I have an old speaker magnet on the bottom of the tube to compensate for the weight of the 22 and 17. The 26 or 31 really are getting a bit heavy. I haven't looked through an Ethos or Delos, but check the weight as well. Some find the Ethos extra wide field is not for them as the eye hunts around the FOV. The Delos with its narrower FOV might be worth considering. I find the 82 degrees of the Naglers is plenty. I would recommend going to a star party if possible before shelling out $$$'s. I have looked through the Pentax 10 XW and the field (about 65 or 68 degrees I think) is ideally suited to the eye and is preferred by many. They are a bit hard to find these days but are a great eyepiece. Much smaller and lighter than the heavier Televue products. There are plenty of threads on this site about eyepiece selections by observers with much more experience and technical knowledge then me. I would recommend scanning through these threads before spending money. I like to read John Bambury's thoughts on eyepieces. This is just one recent thread:
You don't have to stick to the same manufacturer and starting with a couple of eyepieces is sensible. At the end of the day eyepiece selection is a very personal thing and trying before you buy is much to be recommended. Good luck with your selection. Paul.
29-06-2012, 05:03 PM
The situation is a little clearer. The factors to consider when choosing between the 10 and 12" dobs in my opinion are.
1) Light gathering. There is a noticable difference and at 12" the are a lot of faint fuzzies that bcome available. But if I was only an occasional observer and was doing imaging as well, I would probably only be looking for brighter objects, and the 10" will still give great views.
2) Size and physical capacity. 8" and 10" dobs are still easily handled if you have any physical issues. I know some women have trouble with 12" and if you have back trouble a 12" would be hard to handle.
Weighing up these factors against $1000 is something you need to decide.
With EPs, I believe the best option is a selection of EPs giving a variety of powers. The 2 options you gave had powers of 96 and 93 respectively, so probably much of a muchness. I use a 17mm Ethos as my main EP these days which gives 88x but with a 1deg FOV which I use probably 80-90% of the time.
Hey guys sorry for the late reply, been busy with work.
Yup I went down to the shops to check out the 22T4 as well as other EPs from TV. I've been spoiled with 24mm of eye relief with my current 36mm EP, and 20mm from my 17mm EP. The 22T4 was by far the most comfortable, it felt really good to look through it (Plus 80 Deg turned out to be plenty!). The Delos was also nice, but the Ethos was really bad IMHO. I find the Eye relief to be nowhere near as comfortable as the others, and for me thats a big deal. Hopefully Ill be going to a few star parties and check them out in action, but honestly considering the $$$ and the coma the Dob would give at the edges, not sure if the Ethos is worth it.
I think you hit the nail on the head. For casual observing (which really is enough for me) I do think the 10" would be better. I do have a slight lower back issue too, so that was something I always had against the 12". I dont plan on going to any dark sites and with imaging and clear nights in melbourne far and wide, the 10" should be more than enough. I think i'd rather just keep the $1000 and just save it!
Thanks alot guys for your help, its why I love IIS. Once I get the 10", might go with a 22T4 Nagler and get a 13mm Delos, but might just wait till I can see for myself at star parties before committing.
Going along with what Paul said, I too am finding the 10mm (120x) on my 10" dob hits the spot nicely for galaxies (and sometimes the 7mm).
Regarding eyepieces, just throwing in my two cents worth here, drawn from my own experience ...
The first one I'd be buying is a replacement for the 10mm 55deg fov plossl that's sold with a dob telescope. I found it didn't fit many things in it's little fov (large globular clusters amongst them), I would lose objects easily as they travel across the fov, had trouble finding things, and the tight eye relief was the last straw- very uncomfortable for me in every way possible was this little plossl. Since I bought my Pentax XW10mm over 2 years ago, it's been my most used and loved eyepiece. And! It doesn't fog up due to it's weatherproof construction. :D
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