We would like to know what High Power range EP we would need with our 12" f/5 Dob for close encounters with Galaxies.
We have the Pentax 10mm XW and wonder if we can enjoy a higher magnification on Galaxies perhaps in the 6-7mm range. We know that the high power EP's work well on planets and we know we will see a Galaxy larger but will we see more detail on a Galaxy with that power ??
Close to the money but not quite. Whilst the galactic image itself dims as you increase the magnification, the contrast increases, providing additional subtle detail not obtainable at lower magnifications. There is a lot to be gained by cranking up the magnification on galaxies, particularly in larger scopes. The 12" scope Barb and Dave have is ideal and can certainly cope with a lot more magnification on galaxies, than they are throwing at them at the moment. There is always a "cut off point" where the returns diminish, but at present they are far from it.
Barb/David
If you like the 10mm Pentax XW there is no point considering anything other than the 7mm Pentax XW. These are 2 of the best eyepieces ever made at any price IMO. The 7mm Pentax XW is every bit as good as the 10mm and will provide 215X in your scope, which will be ideal not only for your galaxy work but all other medium/high power observing. At some time in the future you should also consider the 5mm Pentax XW, this will give you 300X for those nights of good seeing. It's worth noting that you can still run fairly high power on galaxies, when those powers would not normally be usable on planets and double stars due to poor seeing.
Absolutely agree with Ausastronomer, don't be afraid to use a fairly high power on galaxies if conditions permit. Long ago I took the advice of E J Hartung in his book Astronomical Objects for Southern Telescopes; he noticed that a power of about 5 times the aperture in centimeters brought out the best in faint objects. How right he was, this worked out to 100x in my old 8" scope and I used to increase this to 150x in good conditions. This increases contrast which brings out more detail.
Thanks John ... the contrast and brightness is something we weren't sure of when we increased magnification on Galaxies. Another thing is as you know we are in the older age bracket hmmmm and wondered if we would reach a point where we may over magnify for our eyesight capabilities
May I offer a suggestion for a fantastic High Mag Galaxy EP.
It is the Takahashi 7.5mm ED LE.
This particular EP has an 'ED' lense and gives incredible contrast and crisp image! In the GS 12" Dob at such a high mag it was amazing to see detail in NGC 4945 for the first time. This was after testing many different EP's at our astronomy Camps.
The 'LE' means long eye releif and it proved to be true. It was a very comfortable EP to use giving zero eye strain on the 3 of us that tested it in the 12".
12" at f5 is not an easy scope to get high mag detail. They are better known for their wider fields with EP's around 9mm and up to about 32mm. It is only when you get to your higher quality and price EP's that such crisp detail and amazing contrast is evident, and the Tak 7.5mm has proven to be the best tested in the GS 12" on this testing occasion.
Below I have attached a composite example showing exactly what we observed in March 2006 here in dark skies using the Tak 7.5mm ED LE with 10/10 Transparency and 8-9/10 seeing. The composite shows exactly the way I saw NGC 4945. I made sure I made it looks exactly the way I saw it. I cannot speak as to the quality observed by Darren and Peter but both were more than amazed at the quality of the Tak in the 12".
Thanks Ken for taking the time to reply to our thread with your attachment
We noticed you have mentioned the Tak 7.5 a number of times on different threads. If as you say the image you have included is exactly as you saw it that's really impressive
We're hoping to get to Snake Valley sometime soon and we can catch up with you there.
now you have given me a headache
I dont really assume i am correct despite what i say, i just say what sounds logical... logic isnt always correct, especially when you havent all the information
anyhow, my most humble appologies to both barb and dave
and wondered if we would reach a point where we may over magnify for our eyesight capabilities
Barb & David
Barb & David,
As you get older you develop "floaters". These manifest in the eyepiece as dark "blobs" that seem to float around and block the image. They are a major pain, if you suffer from them bad. They are caused by floating debris in your own eye. Everyone gets them to a degree, but for some people they are a non issue, for others they are a major issue. If you develop them, they get a little worse as you get older. They appear to get worse as you increase magnification but this is actually caused because the exit pupil gets smaller as the magnification is increased. It is not caused by the increased magnification itself. The smaller the exit pupil created by the eyepiece, the worse the effect of floaters.
There are a couple of ways to "minimise" them.
1) Stick with an exit pupil of 1mm or bigger. This means in your 12"/f5 scope you should stick with an eyepiece having a focal length of 5mm or longer.
2) Use a binoviewer. "Floaters" tend not to be such a problem when you are observing with both eyes.
Nothing to worry about, but it helps to be aware of them so when you do see them, you know what's going on.
As John has said you can not go past the 7 mm Pentax.
I would recommend the Vixen LVW but it does not have a 7 mm and the 8 mm LVW is a bit close to your 10mm Pentax.
I don’t think and correct me if I’m wrong, but the Takahashi LE range of eyepieces do not have a threaded bottom barrel.
So you can not screw filters into the bottom barrel.
You may one day find you would like to do this for faint Planetary Nebula.
Thanks Dave we didn't realise that the Tak doesn't have a thread for filters.............something to consider. Yes the 8 is a bit close to the 10. We know the Vixen are great EP's as well.
and wondered if we would reach a point where we may over magnify for our eyesight capabilities
well I did say i could be wrong 
