Should I upgrade my eyepiece for DSO viewing?

[BogdanMD]

Hello, 

Last night I've made my first observation of the deep sky, I was looking at Saturn and Jupiter and noticed that the moon had not risen yet and the sky was darker than usual (I live in the light polluted city). I'm using a Skywatcher 6" Newtonian with the stock eyepiece (Apex 28mm 57 degree FOV).

While I didn't had much success spotting DSO's, partly due to my inexperience (found M22 and Sagittarius star cloud), I think I had trouble star hoping also because of the "narrow" FOV. So I'm thinking about buying a new medium budget eyepiece in the 80-100 degree range. I found the 82 degree series from Explore Scientific which seem to be well regarded.

My question is, beside the larger FOV, are there any other benefits from getting a more expensive eyepiece? Mainly, will it make small DSO's easier to spot? Also, if you have other suggestions for eyepieces that would do a good job, please share. Thanks!

Edited August 10, 2020 by BogdanMD

[Louis D]

If you go to a wider apparent FOV (AFOV) while maintaining the same eyepiece focal length, you'll see a greater true FOV (TFOV) without increasing sky brightness which does increase contrast and makes it easier to spot faint fuzzies.  That's why the 21mm Ethos is more desired than the 31mm Nagler T5 which is itself more desired than the 41mm Panoptic (aside from the desirability of wider and wider AFOVs).  Each step yields slightly less TFOV, but the sky darkens noticeable at each step as well.  Alternatively, when using nebula filters, the lower the power, the larger the exit pupil, the brighter the nebula appears per unit area.  Since the filter blocks most of the light pollution, the contrast get higher at lower powers.

[BogdanMD]

I'm afraid I don't quite understand what you mean. So a wider AFOV at the same focal length will provide a better image (higher TFOV, increased contrast), that's reason enough to upgrade.

I don't understand why should I go for the 21mm compared to the 31mm or 41mm? My understanding was that lower focal length means smaller exit pupil -> darker image, harder to spot dim objects. If I'm trying to avoid that, shouldn't I pick the larger focal length and only switch to a smaller one to get better details on bright DSO's?

Also, having the eyepiece darken the sky is something I want? Wouldn't that also darken everything else?

Apologies for the silly questions.

I assume you gave them as examples to your point but Tele Vue optics are too expensive for my budget (~300$).

Edited August 10, 2020 by BogdanMD

[John]

I find that using a higher magnification with a wider field of view helps me to find faint objects a little easier because the background sky is darkened enabling the deep sky objects to be just that little bit easier to spot. I observe mostly from an area with some light pollution. I have 40mm, 31mm and 21mm eyepieces which all show around the same amount of sky. The 21mm (which happens to be an Ethos) is that one that gets used the most for deep sky sessions.

The 20mm Myriad or APM 100 degree eyepieces are a lot less expensive than the Ethos 21.

The scope that I would be using mostly for this is a 12 inch F/5.3 dobsonian.

 

 

[BogdanMD]

Thank you! I think that's what Louis meant as well, have a darker background without losing too much light coming from the DSO. I'll check out your suggestions as well.

[Pixies]

Having started recently, like you, I found star-hopping tricky to start with. I think the mistake I was making, was to expect to be able to do a lot of star-hopping from the eyepiece. The view is so tight and magnified that it is hard to correlate with whatever star chart you are referring to. I'm sure those with much more experience than me (most here) have better success with this, but speaking as a newbie, this was the hardest and most frustrating part for me. Just one knock and I had to start from scratch. There is very little chance of working out where you are in the sky from the EP view.

I found that it was quicker and easier if you could get pretty close to the final location using the finder(s). If the object is in the FOV of the widest-angle EP when you first look, then it's as good as done. Even if it's hard to see a faint DSO, at least you will be able to match the stars you can see with those in the starchart you are using. The game-changer for me was to use a non-magnifying finder (a Telrad in my case) along with a good magnifying finder (a RACI). The Telrad means I can get straight onto the location of the nearest visible star, then the RACI finder is easy to hop using medium magnitude stars - but perhaps those not visible to the naked eye. Being a RACI means that I'm not on my knees either. For simple objects, like planets, just the Telrad is enough.

Sorry if I am teaching granny to suck eggs! (not sure what that really means - but I'm sure you get the drift)

 

 

[BogdanMD]

@Pixies Yes, you are absolutely right, I've taken another look last night and used the finder scope more, it was certainly easier to move from one star to the next since most of the bright stars I look for are visible on the small scope also. I haven't thought about changing the finder scope and attaching another one doesn't seem possible on my telescope, at least not without some DIY. 

As a side note to my original post, I've noticed that the 28mm 2" EP shows a better image than the 25mm 1.25" EP (Skywatcher Planetary UWA) , the stars look brighter and their colors are easier to distinguish.  So I guess I should be looking for a 2" EP when I upgrade.

Edited August 11, 2020 by BogdanMD