TV 55mm plossl in a 10"SCT f/10?

[Moontanner (Ross)]

Hi all,
I've been stuck at home due to the severe storms in Sydney over the last few days, and as with all good hobbyist's I've been pondering ways to upgrade my astronomy gear. There also happens to be a lot of good gear on the classifieds at the moment which leads me to my question:

Is the 55mm TV plossl a good wide field choice for my LX200gps 10"?

I've read plenty of good reviews on the eyepiece being used in slow scopes such as mine and it's in a reasonable price range.
At this point in time I have the 6.3xFR, TV 2x PM 2", the Eye opener and a couple of bandwidth filters to use in conjunction with this eyepiece( if possible). In time I intend to get a 4x PM to use with the DSLR. Can these items all be used with this 55mm and still achieve a high quality view?

I'd like my kit to be as flexible as possible without wasting a load of money on dozens of eyepieces I'll rarely use. A little basic imaging with my DSLR, plenty of planetary/lunar viewing from my terrace and the odd bit of dark site use when the situation allows would be enough.

I already have various entry level eyepieces so I'm not desperate to get something today. There's the 8mm Stratus, 12.5mm edge on, 30mm Superview with camera projection and the 42mm Superview to keep me content for the time being.

Thanks for any advice. Hopefully, there's enough information about my situation and expectations to get the ball rolling. If there is anything missing let me know.

Ross.

[mental4astro (Alexander)]

Hi Ross,

The 55mm plossl will work well in your 10" SCT. But there are some things you will need to keep in mind with it. I have a 50mm plossl that uses Pentax glass, and I've used 65mm, 75mm & 85mm plossls in my Newtonians and SCT, and they all have the same things to keep in mind (leaving exit pupil aside).

1, These very long focal length eyepieces won't show you anymore of they sky than your 42mm Superview. No matter what you do, the 2" barrel will be the limiting factor here and to a lesser extent the bore in the primary mirror. So, as you increase focal length, you make the AFOV smaller and smaller. My 50mm Plossl has an AFOV of around 50deg. The 65mm has an AFOV of 38deg. And both show the exact same amount of true field of view of the sky. See what I mean?

2, Such long focal length EPs are only dark sky site propositions. They concentrate the background sky glow of urban skies so much that it washes out fainter stars. But, under a dark sky, man-oh-man, they are lovely!

3, Eye relief on such EPs is VERY LONG. The eye relief on my 50mm plossl is close to 30mm - move in closer and you won't see the whole field of view. The 85mm I tried had eye relief of some 70mm! That's how far your eye had to be from the eye lens to look into the eyepiece! I don't have a problem with this, and it just takes a little getting used to.

I can't speak for the Eye Opener as I'v never used one. Someone else may be able to help. The focal reducer won't help you as the AFOV will just be tiny as a result. Exit pupil will exceed 7mm with it, but I am no conformist when it comes to exit pupil - I am happy to use my 50mm plossl in my 17.5" f/4.5 dob. This combo gives me an exit pupil of 11mm, but the image this plossl throws up is gorgeous! Sure you can use the Power Mates with the 55mm, but why would you? You are just adding more glass between you and the sky when other shorter eyepieces will work better.

On its own the 55mm would be a fine piece in your scope. With the other eyepieces you have, coupling it up to other bits and pieces really won't help. I hope this helps you.

Mental.

[Moontanner (Ross)]

Hi Mental,
Most of that makes sense. I'm still getting my head around the way optics work.

1. I get what you mean about the longer focal lengths and the AFOV and wasn't expecting to see any more sky than I get with the 42mm SV. The view through either of the SV's is big enough. Do you think the TV 55mm plossl would yield noticeably better views due to the better quality glass?

2. Point taken on the "dark sky only" usage. I guess that's where my question about the 55mm sprouted from.
If it's only use is to be "as is" on the lucky occasions I get to be at a dark site, I wonder why it seems to be so highly recommended?
Is it really worth it for those rare occasions( subjective, I know)?
Does the darkened sky background possible with a higher magnification and larger AFOV have any negative effect on the view of some objects?

3. Those eye relief figures are definitely up there. Does anyone know if the eyecup is big enough on the 55mm TV?

You've given me some good points to ponder Alex.

The focal reducer was really only ever bought for the camera so I never bothered looking up the affect it would have on the AFOV through an eyepiece. My brain is going to need a bit of time out to reshuffle what I've learned so far.

At this stage I'm happy to save up my pennies for something that will be more useful with my equipment. I was really hoping to be able to limit my eyepieces to 2x you beauties and the 2x powermate. From what I've read this is not unreasonable.
That doesn't include the desire to constantly chase the next best thing.

Thanks for the food for thought.

PS. The eye opener is just a fitting that goes on the back of 10"+ Scopes to give you a 2" opening to work with. It's a little bit bigger than the standard fitting so you can squeeze out a little more FOV. Supposedly they can also add unwanted light in certain situation.

[Renato1 (Renato)]

I've got a 56mm Meade Plossl, and the view in an SCT relative to using a wideangle 40mm 2" eyepiece is like looking down a well. I always prefer the 40mm eyepiece.

There may be some obscure nebula somewhere where with an O-111 or H-Beta filter you can see it better because of the brighter image from the 55mm Plossl. But you will get the same result with a higher powered eyepiece coupled with you focal reducer (and a black cloth thrown over your head and around the eyepiece).

If you have lousy eyesight (e.g. astigmatism) than the shallow eye relief from a wideangle 40mm eyepiece might not allow you to wear eyeglasses while viewing. In that case, the 55mm Plossl could be better as you could easily wear eyeglasses. But I have lousy astigmatic eyesight, and I still prefer the 40mm wideangle or 30mm ultra-wideangle in my SCT.

I guess what I'm saying is that if curiosity gets the best of you, don't spend big bucks on a premium model, rather wait patiently for a cheap second hand one.

My favourite eyepiece in my 8" SCT has always been a 1.25" wide angle 20mm one for DSOs, since it gives a 2mm exit pupil. I note that you don't have a near 2mm exit pupil eyepiece.

My favourite eyepiece for wide angle viewing is a cheap 2" 30mm Ultra wideangle (cost me $80). It is a terrible eyepiece in shorter focal length eyepieces, but as I'm not fussy about edge distortion in ultra-wide angle eyepieces, I think it fine in the SCT.
Regards,
Renato

[Renato1 (Renato)]

Originally Posted by mental4astro

I am happy to use my 50mm plossl in my 17.5" f/4.5 dob. This combo gives me an exit pupil of 11mm, but the image this plossl throws up is gorgeous!
Mental.

Finally - someone else who does the same as me. I use a 40mm wideangle eyepiece in my 14.5" f/4.5 dob which gives nearly 9mm exit pupil.

All the books say not to do, but the view is great - especially with a broadband filter to reduce the sky glow at a dark site. I've gotten slightly dizzy just randomly roaming the Milky Way with it.

The other big advantage is that I tilt my eye at the right angle, and the astigmatism from my eye disappears without blanking out part of the image.
Regards,
Renato

[Visionary (David)]

Renato1,
I am certain this observation throws my raw Newbie status into sharp relief, but I had not thought of a dark cover over the head, BB Bloody brilliant!

[Moontanner (Ross)]

Originally Posted by Visionary

Renato1,
I am certain this observation throws my raw Newbie status into sharp relief, but I had not thought of a dark cover over the head, BB Bloody brilliant!

I can hear the neighbours now.... The looks I get are strange enough as it is with the telescope and the brewery setup in the garage.
It's a good idea but I'll be saving that one for the very private yard I use occasionally.

Renato, thanks for the input. I'm definitely not looking at buying the 55mm plossl straight away (if ever now).

I did pull out all of my eyepieces and have a serious go with each of them while looking at the figures for each. While I'm happy with most of them for the basic stuff, there are a few problems with the views at the edge of field on the superviews that I'm not happy with.

Is it the scope or the eyepiece? I'll be stuffed if I know but I'll be keeping at it until I narrow down the source. If it turns out to be the eyepieces I'll be saving up for a couple of gooduns.

It's funny you mention the lack of a 20mm eyepiece. I was recently drooling over the 21mm Ethos and thinking it would be a useful bit of kit.
On it's own for DSOs and coupled with the powermate for planetary/lunar use.

The Explore scientific offerings looks the goods also.

Anyone want to give me a couple of grand for doing nothing?

Clear skies. I'm getting back to work.

[Camelopardalis (Dunk)]

Ross, depending on which type of tube you have, ACF of not, the issues at the edge of field might be the scope, eyepiece or both.

I've looked through an ACF or two and they're pretty good when pushing the max FOV...not quite as good as an Edge HD but decent.

If you're scope is not the ACF variety it could be the coma from the scope rearing its ugly head. Probably a better idea than spending a lot of $$ on a high-end eyepiece at the moment would be to take your scope along to one of the Sydney area events when they crop up, as there's always someone with quality glass around and if you ask them nicely they're usually open to scientific experiments

[Moontanner (Ross)]

Originally Posted by Camelopardalis

Ross, depending on which type of tube you have, ACF of not, the issues at the edge of field might be the scope, eyepiece or both.

I've looked through an ACF or two and they're pretty good when pushing the max FOV...not quite as good as an Edge HD but decent.

If you're scope is not the ACF variety it could be the coma from the scope rearing its ugly head. Probably a better idea than spending a lot of $$ on a high-end eyepiece at the moment would be to take your scope along to one of the Sydney area events when they crop up, as there's always someone with quality glass around and if you ask them nicely they're usually open to scientific experiments

Hi Dunk, the scope is one of the older GPS models so it's quite possible that the mushy image at the edge of the field is the scope.
From what I've read the 6.3x focal reducer/ field flattener should help with cleaning this up? The sky is looking pretty clear tonight for a test run on that one.

Alas, at this point in time I don't have the spare time to get out to a meeting. SWMBO is about ready to burst with our first so taking off into the night is out of the question for now, along with buying a new scope.
I can probably sneak an eyepiece through.......

Getting back to the AFOV advice, when using the Orion Edge On Planetary 12.5mm eyepiece at 55deg AFOV it was good to get a feel for the tunnel effect. It's a good eyepiece for planetary/lunar observations but lacks the wide open feel of the others. I guess that sums up which way I'm leaning on the 55mm TV Plossl.
(for any other newbies: nothing wrong with the Orion eyepiece. It's great for planetary stuff and works a treat in the 2x Powermate if the conditions permit. In fact I prefer it at 2x to the Stratus 8mm at 1x).

Thanks for all the useful advice so far.
Ross.

[Camelopardalis (Dunk)]

Originally Posted by Moontanner

Hi Dunk, the scope is one of the older GPS models so it's quite possible that the mushy image at the edge of the field is the scope.
From what I've read the 6.3x focal reducer/ field flattener should help with cleaning this up? The sky is looking pretty clear tonight for a test run on that one.

Help...maybe. Eliminate...no chance

You might want to try the same eyepiece with and without the reducer to see the different effect.

[Moontanner (Ross)]

Originally Posted by Camelopardalis

Help...maybe. Eliminate...no chance

You might want to try the same eyepiece with and without the reducer to see the different effect.

As luck might have it the moon was just in view for a test run earlier. I noticed a slight improvement with the FR.

One thing I did notice was that the edge of field view was better on one side while the other was still slightly off. Maybe time to look at fine tuning the scope itself?

You've gotta love a hobby that keeps you endlessly entertained.

[mental4astro (Alexander)]

Ross, going back to the questions you asked me:

1, the image will be brighter, but mainly because the image will be concentrated into a smaller area. Glass and coating quality may have an influence.

2, Worth it? I can only speak for myself. For me yes. But I also recognize that this EP is a folly for me. I don't blindly follow doctrine or orthodoxy - life is so much sweeter and interesting by stepping outside the square .

And yes, there are some objects that do suffer from more magnification (not so much with larger FOV). There are objects that are best viewed with smaller aperture and bugger all magnification, like the Rosette Nebula. This nebula is so large and its light so diluted as a result, that it can be impossible to see in larger apertures because of the intrinsic magnification. You will easily see the Rosette in a pair of 11X70 binos, & have no chance in an 8" SCT with "typical" eyepieces. A 50mm gives you a fighting chance.

3, I can't answer that one as I don't know.

Mental.

[Renato1 (Renato)]

Originally Posted by Visionary

Renato1,
I am certain this observation throws my raw Newbie status into sharp relief, but I had not thought of a dark cover over the head, BB Bloody brilliant!

I read the technique in two books. I went to Kmart and checked their black cloths by holding them up to the block overhead lights. The light easily went through three of the cloths, but one piece of cloth blocked the light completely and that's what I bought.

Though, if you want to check the technique out, just use a light towel or small blanket in the first instance - as you might find the technique annoying - though the black cloth doesn't cost much.

I found it handy when inconsiderate neighbours kept their spot lights on all night, and for seeing really faint stuff out at a dark site when pushing the limits of my 8" telescope. I was able to see the Horsehead nebula in my C8 with a H-beta filter, 40mm eyepiece and a focal reducer and blocking all stray light from the sides (of course, it was a cinch seeing it later when i got a 14.5" dob).
Regards,
Renato

[Renato1 (Renato)]

Originally Posted by Moontanner

I can hear the neighbours now.... The looks I get are strange enough as it is with the telescope and the brewery setup in the garage.
It's a good idea but I'll be saving that one for the very private yard I use occasionally.

Renato, thanks for the input. I'm definitely not looking at buying the 55mm plossl straight away (if ever now).

I did pull out all of my eyepieces and have a serious go with each of them while looking at the figures for each. While I'm happy with most of them for the basic stuff, there are a few problems with the views at the edge of field on the superviews that I'm not happy with.

Is it the scope or the eyepiece? I'll be stuffed if I know but I'll be keeping at it until I narrow down the source. If it turns out to be the eyepieces I'll be saving up for a couple of gooduns.

It's funny you mention the lack of a 20mm eyepiece. I was recently drooling over the 21mm Ethos and thinking it would be a useful bit of kit.
On it's own for DSOs and coupled with the powermate for planetary/lunar use.

The Explore scientific offerings looks the goods also.

Anyone want to give me a couple of grand for doing nothing?

Clear skies. I'm getting back to work.

I have the 30mm Superview projection eyepiece, and it has bad edge problems compared to the 32mm GSO 2" SuperPlossl, which may explain some of your dissatisfaction.

Basically though, you have to remember that unless you spend lots of dollars, edge performance on wide angle eyepieces may be problematic, though things are much better now than when I first started with them 20 years ago.

I found over a 1000 galaxies in my C8 using just a 1.25" 20mm Erfle, where its edge performance being somewhat poor, didn't bother me. A few years ago I bought one of those flat field 19mm 1.25" eyepieces made under various brand names, which gave much better edge performance (cheapest one is the Orbinar one, though I have the Smart Astronomy one).

I also have the ultra wide angle Celestron 23mm 2" Luminos - eye relief is a bit shallow, and the eyepiece is very, very heavy. It gives good views, but for galaxy hunting I'd use my earlier, less awkward to use, 19 or 20mm eyepieces.

I've never looked into an Ethos - but I know that it is very heavy. Having it sitting in a Powermate would worry me. I hate it when I have a heavy eyepiece in the SCT, and inevitably something in the diagonal comes loose and the eyepiece swings upside down. I tend to save the heavy eyepieces for my bigger dob.

Regards,
Renato

[Camelopardalis (Dunk)]

IMO a 21 Ethos would be a waste of field stop...the reducer you're using makes the light cone steeper (making it faster!) so at the same time the useful field stop of the eyepiece shrinks too. The wider you try to go the more you'll see issues.

I've read people say the 17mm Ethos with the reducer is a good combination, but never used it myself. At native f/10 it works well, but there are much less expensive options to achieve more or less the same thing.

[Moontanner (Ross)]

Originally Posted by Camelopardalis

IMO a 21 Ethos would be a waste of field stop...the reducer you're using makes the light cone steeper (making it faster!) so at the same time the useful field stop of the eyepiece shrinks too. The wider you try to go the more you'll see issues.

I've read people say the 17mm Ethos with the reducer is a good combination, but never used it myself. At native f/10 it works well, but there are much less expensive options to achieve more or less the same thing.

Hi Dunk, I wasn't intending to use the focal reducer with the 21mm eyepiece. The 2x Powermate would be the item I'd hope to use with the eyepiece for visual use. Only if I wanted more magnification.
I know it's an expensive piece of kit. I was thinking it might be a one stop shop when used by itself or with the 2x Powermate. 21mm and 10.5mm.

[Moontanner (Ross)]

Alex, Life is best when you have a Folly. I try to have at least three or four in reserve. Just in case one comes good.
I'm still tempted to get a long focal length plossl for the one time I do get to a truly dark site on a truly brilliant night.

Renato, I'm not overly stressed about the weight as my work involves dealing with far worse. I definitely get your point though.
Point also taken on the whole branding thing too. It's good to know that there are plenty of other options out there that will get the job done.

[Camelopardalis (Dunk)]

Originally Posted by Moontanner

Hi Dunk, I wasn't intending to use the focal reducer with the 21mm eyepiece. The 2x Powermate would be the item I'd hope to use with the eyepiece for visual use. Only if I wanted more magnification.
I know it's an expensive piece of kit. I was thinking it might be a one stop shop when used by itself or with the 2x Powermate. 21mm and 10.5mm.

I still reckon an ES 30mm would serve you better, and save a ton of $$.

Then get yourself a small ~10mm for planetary, and save yourself some heart ache. When you see and feel the size and weight of the Ethos 21 let alone the 2" powermate you'll understand

[Moontanner (Ross)]

Originally Posted by Camelopardalis

I still reckon an ES 30mm would serve you better, and save a ton of $$.

Then get yourself a small ~10mm for planetary, and save yourself some heart ache. When you see and feel the size and weight of the Ethos 21 let alone the 2" powermate you'll understand

Where does one look to buy the ES range? Are they available locally?

While happy to take peoples advice and factor in the sheer weight of some of theses premium eyepieces, I can't see it being much worse than strapping the camera on.
You also get the added bonus of having a heavy blunt object on hand. This could come in handy when I'm being attacked in a remote location at night while wearing a dark cloth over my head.

[Camelopardalis (Dunk)]

VTI optics stock some of the range, it might be worth contacting them and asking if they have an 30s coming in soon. Failing that, there are some good choices from the US...different folks have their own experiences/preferences

From a stability point of view, it's quite different...with the camera on the back, you're using adapters that are all screw threaded so they don't budge and it's almost impossible for them to detach. With eyepieces, you're relying on multiple relatively small compression rings...it only takes one to loosen or slip and...thud