High Power EP's For Galaxies ?

[Tamtarn]

We need some more advise guys :help:

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 ??

Your opinions will be greatly appreciated.

Barb

[ving]

the image by rights should be dimmer showing less detail... I'd think there would be a fine balance between magnification and brightness...

[Tamtarn]

Thanks Ving

Thats the type of feedback I want

Barb

[ving]

no problem, i assume i am correct but if i am wrong someone will correct me :)

use www.scopesim.com to show you the effects of magnification on brightness.

[ausastronomer]

Vingo,

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.

CS-John B

[Scoper]

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.

[Tamtarn]

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 :whistle: and wondered if we would reach a point where we may over magnify for our eyesight capabilities

Barb & David

[ballaratdragons]

Barb,

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".

(I sound like a Tak salesman) :lol:

[matt]

Wow!

I've never seen a galaxy look that bright through the eyepiece:scared:

That's really how bright the lighter areas of the galaxy appear with that scope/ep combo?

And you didn't even use a UHC or OIII filter!

[ballaratdragons]

I don't own any filters Matt. Yep, it looks that good, but not with the El-Cheapo GS or Series 500 crappo's.

And ya gotta have reasonably dark skies :thumbsup:

Poor seeing doesn't seem to make much difference which is good!

[Tamtarn]

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 :2thumbs:

We're hoping to get to Snake Valley sometime soon and we can catch up with you there.

Barb & David

[ving]

lol, oops...
looks like i was leading you ashtray :rolleyes: well I did say i could be wrong :(
sorry bout that.

[matt]

Yes. That's the peril of assuming you are correct .... even while suspecting there's a chance you'll be corrected:lol:

I think it's safer if we assume you're wrong, in the first instance, while we're awaiting confirmation lol

[ving]

now you have given me a headache :P
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 :rolleyes:

anyhow, my most humble appologies to both barb and dave :)

[matt]

not nearly as big a headache as you've caused...hahahaha;)

[ausastronomer]

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.

CS-John B

[Dave47tuc]

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,:whistle: 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.:)

[Tamtarn]

VING & MATT....... STOP You've got both of us in stitches laughing :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

I had to get David to grab a mountain of tissues for drying the tears of laughter :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:


You're intentions were sincere :thumbsup: :thumbsup: :thumbsup: :thumbsup:

Barb & David

[Tamtarn]

John your answer to our question happens to be spot on.

I already have what you describe as floaters and David has to a lesser extent. It's not a major issue at this stage.

This is why we asked the question about even higher magnification.

Thank you so much John this helps us in knowing our limitations regarding higher power EP's.

Barb & David

[Tamtarn]

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.

Barb & David

[ballaratdragons]

Thanks Dave, I didn't know that either. :thumbsup:

But I am still getting the Tak coz I LOOOOVE the view :)

[johnno]

Ken,
Absolutely loved the photo of NGC 4945,in your earlier post.

WHAT A GREAT SHOT,Thanks.
Regards.John

[CoombellKid]

FWIW for Barb and David's sake, you wouldn't use either of the above filters
on galaxies. Since both filters are designed to cut down star light to enhance
the visible emission lines of nebulous cloud. Galaxies or the light we see from
them is esentially star light, hence you would be blocking the very light your
trying to observe.

regards,CS sunny days

Rob

[matt]

onya rob

Still, it's handy to have either or both those items in your kit for when you want to turn your attention to the objects they are designed for:thumbsup:

[Tamtarn]

Thanks everone . :thumbsup: After a great deal of thought we have decided on the Pentax 7mm XW considering the added FOV and eye relief this particular EP will suit our needs.

We certainly realise that using a filter is totally useless on observing galaxies but we know it would be an advantage for observing Nebula.

All in all we feel the Pentax is just what we need and with the added advantage of the cheaper price at $399 before the upcoming price rise it was too good a deal to miss out on. EP now ordered due to arrive this week. Hoping for better weather. :)



Barb & David

[matt]

Very nice.

Please be sure to give us a thorough first light report.

The 7mm XW will almost certainly be my next ep purchase so I'll be really interested to read your comments:thumbsup: