10 replies to this topic

[Jon Ingram]

Hello all,
I have NO IDEA what to buy when it comes to visual use of my telescope. I have a pretty solid astrophotography set up, but I’ve never done any visual astronomy with it. My son and I would like to look at planets, the moon, and commets when they come around, and maybe anything else that’s bright enough. My primary priorities are ease of use in switching between photography and visual viewing, and versatility and being able to view a wide degree of objects easily. I would be willing to pay a little more to make the transition between the two easier. I don’t want to spend a lot of money, but would be willing to spend up to $500 if I need to achieve those goals. Any suggestions? If I understand it correctly, I would probably need to get some sort of 2 inch diagonal attached to an eye piece? My telescope is an Askar 130 PHQ APO flat field, 1000mm. Thanks in advance for your help and suggestions!
Jon

[MrsM75]

oh my, a $3,500 scope. You going to need premium eyepieces and diagonal through and through, such an expensive scope, I doubt cheap $40 eyepiece would work with it.

 

I let the experience observers answer you, but whoa, pricey scope.

[SeattleScott]

If you really want to be able to swap back and forth, you probably want a flip mirror diagonal with a helical focuser. That way you use the focuser to focus the camera. Then to switch to visual, you flip the mirror (which will cause the camera to go dark) and use the helical focuser to focus the eyepiece. These normally only accept 1.25” eyepieces so you sacrifice max FOV for the convenience of swapping between visual and imaging. But idk, I suppose there might be a 2” one out there.

[Procyon]

You might have better organized nights by splitting the photograph sessions and visual part. Maybe one night visual, one night astrophotography.

Get something like a 2" Baader Clicklock diagonal and a 28mm Astro-Tech 82 eyepiece to start. That'll give you a wide field and keep you near the budget you asked for. Other good choices would be a 31mm TV Nagler, 35mm TV Panoptic, 40mm Pentax XW or 48mm Brandon but those cost more. Just my quick take, haven't used many refractors. Or cameras.

PS> All those eyepieces are for low magnification widefield views, they may work well for some comets though. For planets and the moon, perhaps a 9mm Astro Tech 100 XWA or a 10mm Pentax XW but than you'd also need a 2" to 1.25" eyepiece adapter. For the 10mm Pentax that is.

You can go with much higher magnification with a 4-7mm eyepiece in that scope but than you may not see the entire moon in the view and comets may not look so great. It depends what you want to see more of also, planets, the moon or comets, all require different magx but a 9 or 10mm at about 100x magnification and with a view of 0.7-0.9 degrees might be a jack of all trades for now. You'll be able to see Globular and Open clusters as well.

Edited by Procyon, 29 April 2025 - 09:08 PM.

[davidgmd]

Basically, you need a 2” 90-degree star diagonal and some eyepieces.

 
You don’t have to get premium eyepieces or the world’s best 90 degree star diagonal just because you have an expensive scope. Less expensive stuff will work fine if you’re not demanding perfection. Prices start increasing dramatically for that last few % increase in quality.

   
You mention ease of use as a priority. Scott makes a good point about a flip mirror if you want to be able to shift from AP to visual with just the flip of a switch. That will eat up a bigger chunk of your budget than a decent 2” diagonal and it will limit you to 1.25” eyepieces. I can’t tell from your post if it would be simple and trivial to switch from your AP setup to visual. It will be if all you have to do is remove the camera and spacer from the focuser and insert a diagonal and eyepiece.

    
If you replace the camera with a diagonal and eyepiece, what will you use to find objects? Will you need a finder?

   
For a 90 degree star diagonal, I’d recommend a 2” mirror over a prism for an f/7.7 scope. A prism may add some chromatic aberration on bright objects. I like the Baader ClickLocks but they’ll bust your budget. Tele Vue Everbrite and AP MaxBright are top of line but are also budget busters. You can get very pleasing views with a budget 2” GSO mirror with 92% reflectivity for $80, leaving a nice chunk for eyepieces. Or step up to a 99% reflectivity GSO 2” dielectric mirror diagonal for $119. For most people, it takes an increase in brightness of 8% to be able to see the difference, so you might not appreciate the improvement that much on bright targets. Most 2” diagonals come with a 2” to 1.25” adapter so you can use eyepieces of either size.

  
For eyepieces, a critical question is whether you or your son wear glasses to correct astigmatism. Near- or far-sightedness can be corrected with the focuser, but astigmatism usually requires that glasses be worn at the eyepiece. (Usually because it depends on how much astigmatism and size of the exit pupil, which we can get into later if necessary.) If glasses are needed, eyepieces with long eye relief, usually a minimum of 18-20 mm, will be necessary. If you wear contacts to correct your vision, you don’t need the extra eye relief.  
 
A terrific resource for eyepieces is Don Pensack’s Eyepiece Buyer’s Guide. You can sort the spreadsheet on any parameter to find candidates based on focal length, eye relief, AFOV, etc.
 
You’ll want a 2” long focal length wide field eyepiece for sweeping star fields, large objects, and as a finder if your system for locating objects is not accurate to within a half degree or better. If you don’t need glasses, the Astro-Tech 28 mm UWA with an 82 degree AFOV and 12 mm eye relief is a top-notch choice at $240 from our site sponsor. CN members get a small discount when ordering from Astronomics. A number of other brands offer clones of this eyepiece. You can search the site for more info. If you need more eye relief to work with glasses, the APM 30 mm UFF has a 70 degree AFOV and 22 mm eye relief and costs about $220. Both of these eyepieces are known for having flat fields, so they should play well with your flat field scope.

  
From there, it gets a bit more complicated with innumerable choices of 1.25” eyepiece focal lengths, AFOVs, etc. You’ve got about $200 left of your $500 budget. Enough for 2 or 3 decent quality eyepieces if you don’t need really wide fields. Assuming you have a GEM that tracks for AP, you won’t need wide field eyepieces for small targets like planets since the mount will keep your target centered.
   
Most places, views of planets are limited by seeing (atmospheric stability) to a maximum of around 200X, which would be a 5 mm eyepiece in your scope. If you live in coastal Florida, seeing is better and you might achieve 300X frequently. But if you live under the jet stream, it may be rare for seeing to support even 180X, so a max power eyepiece of 6 mm (167X) might make sense.

  
An intermediate power, say 9 or 10 mm (100-111X) would be good on the Moon, along with your high power eyepiece, for those times when it’s up and AP is less appealing.

  
Some potential candidates for 1.25” single focal length eyepieces that are within your budget are the Astro-Tech Paradigm Duals with 60 degree AFOV and 13 mm eye relief at $70 and the Astro-Tech UWAs with 82 degree AFOV and 12 mm eye relief at $120. The eye relief for both are too short for glasses. Plössls are also within your budget, but have narrower fields and eye relief that is 0.7 time their focal length. If you need to wear glasses for astigmatism, let us know and the folks here can recommend longer eye relief eyepieces.

  
A lot of people like zoom eyepieces. These offer convenience and cover a wide range of powers without having to switch eyepieces or spend the money on multiple single focal length eyepieces. They tend to have narrower AFOVs at the longer end of their focal range and be less well corrected in the peripheral field than the better single focal length eyepieces.

   
A budget zoom that gets a lot of praise here is the Svbony SV135 7-21 mm zoom. Confusingly, there are 3 different eyepieces with this model #. I think it's the 6-element, 4-group one with 40-57 degree AFOV that has garnered the most praise here, but I’m not sure. Eye relief is 13-14 mm. For under $50 and the ease of Amazon returns, what’s not to like? The Svbony SV191 is a 7.2-21.6 mm zoom and offers 18-20 mm eye relief that should be glasses compatible for under $80.

Edited by davidgmd, 01 May 2025 - 07:37 AM.

[davidgmd]

One other difference between AP and visual to consider is balance. Balance doesn’t change suddenly or dramatically during an AP run. With visual, every time you change eyepieces the balance is off because the eyepiece weight goes to zero temporarily and then changes to the weight of the new eyepiece.

  
How much imbalance can the mount handle without losing the target when changing eyepieces? That might influence your eyepiece choices.

Edited by davidgmd, 30 April 2025 - 02:49 PM.

[SeattleScott]

One other difference between AP and visual to consider is balance. Balance doesn’t change suddenly or dramatically during an AP run. With visual, every time you change eyepieces the balance is off because the eyepiece weight goes to zero temporarily and then changes to the weight of the new eyepiece.

How much imbalance can the mount handle without losing the target when changing eyepieces? That might influence your eyepiece choices.

If not using a flip diagonal, then it becomes an issue of shifting balance when pulling of a camera, possible filter wheel and replacing it with a diagonal and eyepiece. Does the mount lock down tight enough to stay on target while dropping the camera gear?

The big problem if you don’t use a flip diagonal is focus. You focus the camera, which isn’t necessarily a trivial matter. Take a few pics. Now you want to take a peek visually, so you drop off the camera, put an eyepiece in and refocus for the eyepiece. And it is unlikely your whole eyepiece set will be parfocal so there is almost no getting around this. Now you put the camera back on, and have to refocus the camera. So it will invariably be a significant hassle to go back and forth between visual and imaging, unless you use a flip diagonal with helical focuser (so you can focus eyepiece independent of camera).

[davidgmd]

Scott, I agree that for switching back and forth during a single session a flip mirror is the way to go. I’m assuming that’s not the plan here, since Jon says that their visual targets will be the Moon and planets, and the occasional comet. Those aren’t the usual suspects for AP. My assumption is that they’ll do either AP or visual on a given night. Or if they switch, it might be once during an evening to do visual either before or after an AP run, maybe depending on where the Moon is. If I’m wrong and they do want to switch back and forth multiple times, I’d also recommend a flip mirror.

  

While the balance point will differ significantly between AP and visual if you replace the imaging train with a diagonal and eyepiece, it only needs to be done once if you mark the spot on the dovetail for each setup.

Edited by davidgmd, 30 April 2025 - 04:07 PM.

[Jon Ingram]

I want to give a huge thank you to everyone who responded to me on this!  You all are great, and this is a wonderful community! To answer some questions about my setup, I'm using a strain-wave mount - so balance hopefully isn't an issue. I'm current auto-guiding with an OAG, but I'm assuming I would need to switch to an external guiding setup for visual use. I wear glasses, but fortunately no astigmatism.

 

@SeattleScott - Thanks for the suggestion on the flip mirror diagonal. That's an interesting idea and makes a lot of sense for ease of transition. Balance isn't currently an issue on my setup as I'm using a strain-wave mount, but this would probably save quite a bit of time with focus and fussing aroudn. My only worry is whether or not the flip-mirror would degrade the photography image at all. I will definitely look into the flip mirrors.  I will probably do visual at the beginning of the night before starting the photography. Thanks again!

 

@Procyon - That's a good point about different nights for photography and visual. I think you might be right about that, especially if I don't go with the flip-mirror. I also appreciate the suggestions for the specific eye-pieces.  

 

@Davidgmd - Thank you for your super helpful and informative response! I'm sure that this saved me hours of research and confusion. I like your suggestion of going with a 2" dialectical mirror diagonal and the astrotech 28mm that both you and Procyon suggested, as well as may a 9-10mm, and a 5mm. Your information about eye relief, seeing conditions, and the size of pieces needed for my scope was very helpful. 

[PKDfan]

Hi Jon Ingram !

Since you have zero practical experience with actually observing your eye is unpracticed with image scales and field brightness -also know as magnifications !
So the purchase of a quality zoom will help guide you into selecting just the right Goldilock powers your eyes see best at.

I let you decide on choices as there are many of them from SvBony to APM & Baader to name a few.

It matters not on apparent field size at this stage in your visual journey so the additional purchase of a good low power as has been suggested is a great idea.

As for dielectrics and spending alot well a box standard GSO is plenty enough to begin so 100dollars is enough.

After some time has passed maybe you'll see the limitations of kit you started with and desire a fancy BBHS Sitall mirror but thats years down the road or maybe you just minimally invest.


And instantly changing powers is a heck of alot of fun.

The name of the Game !


CSS
Lance

Edited by PKDfan, 30 April 2025 - 10:20 PM.

[SeattleScott]

The flip mirror won’t degrade the camera views. It flips out of the way for the camera. The mirror is only used with the eyepiece.

Now it does eat up some focus travel. You want to make sure you can still reach focus.

And I only used it with small sensors. Could there be an issue with clear aperture if you are really maxing out the field of view with a large sensor camera? Idk.