Finderscope vs low power wide field EP

[Matt Ikaruga]

No doubt this has been done to death - apologies in advance. 

 

I appreciate that a Finderscope (depending on specs) should give me a wider FOV, but are there any other benefits I'm missing over a wide field EP? 

My use case, Celestron Astro Fi 6" SCT and I do use the GoTo but seemingly like I read all over the place GoTo's can be less accurate sometimes so a wider field view would still be useful in finding targets it misses. I've got no issues with the RDF for visible objects, works a treat but as I'm a GoTo'er and not someone who can star hop easily I'm looking at ways to help out.

I have a lovely 32mm plossl (looks like the Celestron Omni but has no branding - no idea where I got it but the views are glorious) which gives a fairly wide-ish view but I'm also away the OTA type means a tighter FOV anyway.

Thanks in advance folks.

[M40]

I know where you are coming from and I moved away from the finderscope some while ago and now use an rdf which gets it more or less there, then I move to a 32mm in a flip mirror which gets it in the field of view of either the camera or the zoom. I did use a cross hairs eyepiece, but the batteries run out 🤪

 

 

Edited August 22, 2023 by M40
Speling

[josefk]

Hi there. My two pence for the GOTO use case is that it probably comes down to how often does your GOTO not achieve the target in the ~1-degree FOV you get with a 1500mm focal length and a 32mm/~50-degree TFOV plossl? ...and by how much does it miss? ...and how often are the missed targets bright enough to detect in a finder?

If it's often and so inaccurate that you can't find the target even with a little bit of local sweeping about with that 1-degree EP then a finder may help but it will only help you for objects you can see in the finder. If you can't see them in the EP initially and also can't see them in the finder, you're just looking for their location, then you are already into star hopping and using a star chart to be sure of exactly where you are in any event (and you could anyway do that through the EP if you didn't have to hop far).

Cheers

[Ratlet]

The only downside I've found with using the low power eyepiece instead of a finder is that you get so many stars it can be difficult sometime to figure out where the heck you are.

That being said, I've hardly ever used a finder scope and have been using a 32mm plossl in lieu of a finder since I picked up my quickfinder.  In fact for a while the 32mm plossl was my most used EP.  Love it.

I have had struggles with the AZ-GTI but I've found most of them can be solved once I've aligned by first going to a bright star near the target of interest first.  If the goto misses I can line up on that and resync.  It then usually pootles on over to the target within the 32mm FOV.

[Matt Ikaruga]

Thanks all, really useful and down to earth (...!!!!) responses there which puts me off the scent. 

The GoTo, I'm still getting to grips with accuracy. I put it all away after my initial honeymoon period in late 21/early 22. It's back out but obviously not dark skies at a reasonable hour yet but already having much better luck with aligning. Almost to the point of face palming myself with how the hell was I getting it so wrong before.

 

@josefk think you've nailed it in your last paragraph really. And further than that, if it's missing by a country mile then I need to look at how I'm setting up (level etc) and aligning in the first place as it should be reasonably accurate most of the time.

And @Ratlet sounds like a very similar use case to me so reckon the 32mm may do me for now while I get more nailed on with the GoTo and any quirks in my set up.

 

 

 

[Guest]

I have a Stellarvue 13x80mm finder on my 16 inch go to.  I have definitely been asked why you need a finder on a go to, the answer is alway.... because there will be times I just dont use the go to and because it just looks good sitting there lol. I will agree that I have definitely gotten lost a few times, but eventually you get past that 

[bosun21]

When I use a go to mount I can go through an entire session without even taking the caps off my finder scope. I have found that when I do the alignment process really well (accurately centre the alignment stars) and a good polar alignment I always have my targets in the fov of a 17.5mm eyepiece. When not using a go to mount I predominantly use an accurately aligned RDF which then always puts the target in the eyepiece. My RACI finder comes into play when I need to star hop with my dobsonian to find faint or tight doubles etc.

[glafnazur]

35 minutes ago, bosun21 said:

When I use a go to mount I can go through an entire session without even taking the caps off my finder scope. I have found that when I do the alignment process really well (accurately centre the alignment stars) and a good polar alignment I always have my targets in the fov of a 17.5mm eyepiece. When not using a go to mount I predominantly use an accurately aligned RDF which then always puts the target in the eyepiece. My RACI finder comes into play when I need to star hop with my dobsonian to find faint or tight doubles etc.

Same here, after a good alignment I never need the finderscope.

[Matt Ikaruga]

Great info folks - thanks!

[Louis D]

A separate finder scope can be nice to have to avoid eyepiece swapping and possibly upsetting the aim on an undriven alt-az mount.

[The60mmKid]

This also depends on the telescope in question, the level of light pollution, and the objects that one is trying to find.

Unless you have a small, fast refractor, a finderscope is likely to provide a much wider FOV than just the telescope plus a wide-field eyepiece. The extra FOV is helpful for star hopping since you'll know where you are looking in the sky in relation to the object that you're seeking.

A magnifying finder is also helpful for star hopping under light-polluted skies since it will allow you to see many more stars than a zero-magnification finder (i.e., RDF, Telrad, etc.).

A finderscope is helpful when searching for objects that are more difficult to find since, again, it gives you access to many more stars for star hopping.

[Mr Spock]

In the kind of light polluted skies I have conventional finders are very limited in use. With the 4" I use a RDF to point roughly in the direction of where I want to be. It's only rough because some faint constellations I cant actually see. I then have a wide field 6x30 finder which gets me down to mag 6. But to actually find things I use an eyepiece. A 42mm LVW gets me almost 4°; a 30mm UFF gives nearly 3°.

[John]

I like to have a true field of between 5 and 6 degrees for finding. With a 32mm plossl a 6 inch SCT will give a true field of fractionally over 1 degree so, for me, not enough. I do use a wide field eyepiece for the final stages of finding fainter targets but even then I like to have over 1 degree of true field if at all possible, preferably 2 degrees.

I don't use GOTO systems.

Edited August 22, 2023 by John

[badhex]

I have pretty much exclusively used a 40mm 2" EP for finding/star hopping for the last few years, giving me around 4° TFOV and 6° TFOV in my two most used scopes, all on undriven manual mounts. 

Having no additional equipment to set up, attach and align does simplify things somewhat and helps with potential balance issues, and in general that has been why I've tended to stick with just the widefield EP approach. 

All of that said, that approach is not without its drawbacks so I have experimented a little with a 50mm RACI and also a reflex-type RDF.

There are times when in an unfamiliar bit of the sky where I've switched EPs, only to be confused about what I'm seeing, and then had to drop back down to the 40mm to re-find where I was, which is a bit of a faff, especially since its possible every time you switch EPs that you might knock the scope out of position. It's useful in those circumstances to just be able to look directly in the finder and compare the view with what I'm seeing in the narrower EP. 

I would say that the "best experience" for finding, especially under non-ideal LP, is probably something like @Mr Spock's approach, where you have both RDF and finder, but obviously it's extra stuff to have to do, extra weight etc.

The "simplest setup" approach is just using widefield EP. Then there are the in between options such as just an RDF or finder. 

I've opted in the end to keep an RDF to hand so that I can set it up if I want, or not, without too much extra weight or effort, depending on sky conditions etc, but I often don't use it.