Doublet VS Triplet

[keybaud]

I am a bit of a pedant and have a habit of micro-analysing things I do to a level that is beyond the comprehension of my wife and family, which has meant that I've spent far too long on Google looking at options for novice to astrophotography (yes, I've got and read 'that' book). I recognise that the mount is the most important piece for imagery and I'm probably going to get a HEQ5; however,  I am still looking at suitable telescopes and would be grateful if someone could clarify whether it is worth spending a bit extra on a triplet. It is a bit extra to get a WO GT-81 or a SW Esprit 80ED over a , but as I'll be buying a mount, guide scope and a plethora of other items in the coming months, it isn't an excessive increase on the total cost. On the assumption that I'll continue with the hobby, and get carried away with it, is the triplet worth purchasing or a doublet?

[keybaud]

When I find the option to edit posts, I'll add the missing words to my post above! In the mean time, add them as required!

[steppenwolf]

As with so many pieces of astronomy kit. not all items of a 'type'. are created equal. For example I have a William Optics Megrez 72D which is fabulously built and feels very professional; I also have a Sky-Watcher 80 ED which feels 'OK' but not as well crafted as the Megrez . However,  although these are both ED glass doublets, the optics of the Sky-Watcher outperform the Megrez by a good margin when it comes to chromatic aberration and this alone makes the ED80 a much better choice for imaging.

The same is true of small triplet refractors - just because it has the 'triplet' design is no guarantee of excellent performance so careful research is required.

As it happens, the original WO GT-81 had a pretty good reputation and I have no reason to believe that the current batch do not also perform well so they should be on your shortlist. Given the choice, for imaging, I'd rather have a good triplet that a good ED doublet, of course but good triplets usually come at a somewhat higher cost.

[ronin]

As with so many pieces of astronomy kit. not all items of a 'type'. are created equal. For example I have a William Optics Megrez 72D which is fabulously built and feels very professional; I also have a Sky-Watcher 80 ED which feels 'OK' but not as well crafted as the Megrez . However,  although these are both ED glass doublets, the optics of the Sky-Watcher outperform the Megrez by a good margin when it comes to chromatic aberration and this alone makes the ED80 a much better choice for imaging.

The 80ED is f/7.5 and uses FPL-53, whereas the WO72 is f/6 and the slightly lower spec FPL-51.

The extra speed of the WO72 will be the cause of most of the additional CA that is apparent, can probably ignore the actual glass types used. If you have a good achro at a suitable slow speed the CA is reasonable.

Just seems a bit unfair to come down on one side or the other, especially when both are doublets and the OP's SW-80 alternative is not the Meg72 but a modern FPL-53 triplet.

Mind you WO scopes do not come cheap could ultimately be a big factor. Also add in flatteners.

[swag72]

When I came to changing my Skywatcher scope to a shorter refractor I had a budget of about £1k. In doing my research I was told by many a good imager on this forum that a good doublet is better than a poor triplet. To that end I found and bought a Pentax 75SDHF - A quality doublet. Another doublet I would have considered was a TV85 - Televue is a quality brand.

For £1k I felt that there was too much scope (excuse the pun) to get a poor triplet - I am pleased I took this advice, the little Pentax doublet was a dream.

Over a year later and I feel there are still few triplets I would consider in that sort of price bracket.

I've also been delighted with my 2 second hand scope purchases - the duffest scope of the lot was a brand new Skywatcher. I'm afraid that has probably mace me rather jaded. Do your research and a second hand scope is a good buy.

[lensman57]

I am a bit of a pedant and have a habit of micro-analysing things I do to a level that is beyond the comprehension of my wife and family, which has meant that I've spent far too long on Google looking at options for novice to astrophotography (yes, I've got and read 'that' book). I recognise that the mount is the most important piece for imagery and I'm probably going to get a HEQ5; however,  I am still looking at suitable telescopes and would be grateful if someone could clarify whether it is worth spending a bit extra on a triplet. It is a bit extra to get a WO GT-81 or a SW Esprit 80ED over a , but as I'll be buying a mount, guide scope and a plethora of other items in the coming months, it isn't an excessive increase on the total cost. On the assumption that I'll continue with the hobby, and get carried away with it, is the triplet worth purchasing or a doublet?

Regardless of the type of glass used, fast doublets and triplets have more CA than a scope of similar design and aperture but with a slower F ratio. It is not appropriate to compare these to each other. A good triplet will almost always outperform a doublet of the same aperture and F ratio. Televeue, Takahashi and a couple of other none mass produced brands have a reputation for quality and optical performance at a price of course.

Regards,

A.G

[steppenwolf]

Just seems a bit unfair to come down on one side or the other, especially when both are doublets and the OP's SW-80 alternative is not the Meg72 but a modern FPL-53 triplet.

The point I was trying to make was not to do with the two specific choices  - these are just two examples from my own recent direct experience. I do, of course, agree that the Megrez is faster than the SW and this will clearly impact on CA but the Megrez does not make for a great imaging 'scope whereas the ED80 does.

Something else that I have discovered is that high cost is no guarantee of high quality so pre-purchase research must be taken very seriously indeed!

[Sp@ce_d]

Well, if I had been asked this question at the beginning of November and from my experience of the WO & SW doublets I've used, I'd have said go for the SW 80ED as it has better corrected optics and nothing under a grand will touch it. However, now that I have the Esprit 80 & if your budget will stretch to it my answer would be go for that.. there is no doubt, the tighter stars just make me grin every time I see a sub coming in.  However, you have to take into account the learning curve. The 80ED will almost drive itself.. it's forgiving where the Esprit is not. For instance being a faster scope the Esprit will not tolerate slight mismatches in the spacing distance with the flattener that I get away with on the 80ED. That's my view from the scopes I've owned.

Now, sticking with the choice of WO or SW as you've singled out, that decision I would make on optical quality. If build quality/QA were priority then WO would win... from my personal experience.  So, if you have the budget for it and if I were starting again I'd say the Esprit 80 is the new 80ED.. (but at a higher price & slightly steeper learning curve)  However, I haven't tried the GT81 and I have only been resisting getting one to compare with the Esprit because I keep telling myself I want a longer FL scope for galaxy season.

[m37]

If the rain stops I will post first light images from the GT-81. If it stops. Ever.

[keybaud]

If the rain stops I will post first light images from the GT-81. If it stops. Ever.

I'm off to go and start lots of fires in the vain hope that the sky will dry out for you...

[Tim]

What camera are you planning on using? Mono or colour? Chip size?

Preferred target type?

These are also factors that will help you determine your choice.

I have a Skywatcher Esprit triplet, and the optics are excellent, not a trace of CA. I haven't tried the whole range though.

Also, I hate to say it, but an EQ6 will give you better results than a HEQ5 pro. How "into it" do you think you will get? I ask because my single regret when buying my kit was not going for the EQ6 right from the start.

[keybaud]

What camera are you planning on using? Mono or colour? Chip size?

Preferred target type?

These are also factors that will help you determine your choice.

I have a Skywatcher Esprit triplet, and the optics are excellent, not a trace of CA. I haven't tried the whole range though.

Also, I hate to say it, but an EQ6 will give you better results than a HEQ5 pro. How "into it" do you think you will get? I ask because my single regret when buying my kit was not going for the EQ6 right from the start.

I only have a 70D DSLR at the moment, but I have managed to remove the IR filter on my old ESO 30D. I've read about CCDs, but wanted to wait until I had taken photos with the DSLR before I upgraded to something better.

As for targets, I'd like to photograph galaxies, as there's something special about seeing pictures of them, but I also know that I tend to get carried away once I start something.

[lensman57]

I only have a 70D DSLR at the moment, but I have managed to remove the IR filter on my old ESO 30D. I've read about CCDs, but wanted to wait until I had taken photos with the DSLR before I upgraded to something better.

As for targets, I'd like to photograph galaxies, as there's something special about seeing pictures of them, but I also know that I tend to get carried away once I start something.

Hi,

If your imaging love is the Glaxies then to image these well you'd have to go deep and for this you need long FL, the popular choice is the SCTs with a 0.63 FF/FR to bring them to about F6.3 so for an 8" you'd be at about 50" of FL,  with the exception of M31 and M33 the rest of theses beauties are far too small to be imaged with short FL 80mm fracs. Something that you have to be aware of.

A.G

Edited December 22, 2013 by lensman57

[Sp@ce_d]

Have a play with a FOV calc. http://www.12dstring.me.uk/fovcalc.php & see how your favourite targets look. As said, aside from a very few, most galaxies require a longer FL than the scopes you're considering, to do them justice.  This also brings with it a steeper learning curve as things like flexure & guiding accuracy become much more critical. It also means as mentioned before you will really need to go up to a higher spec mount, EQ6 at minimum.

So, going back to the original question, if you were to go for a refractor you would want good correction as you'll be shooting either LRGB (with maybe some Ha) or One Shot Colour (DSLR) for galaxies. Yes, you probably are looking at a triplet at the FL needed but it quickly starts to get expensive. However, refractors are regarded as more 'works out of the box'.

[keybaud]

Have a play with a FOV calc. http://www.12dstring.me.uk/fovcalc.php & see how your favourite targets look. As said, aside from a very few, most galaxies require a longer FL than the scopes you're considering, to do them justice.  This also brings with it a steeper learning curve as things like flexure & guiding accuracy become much more critical. It also means as mentioned before you will really need to go up to a higher spec mount, EQ6 at minimum.

So, going back to the original question, if you were to go for a refractor you would want good correction as you'll be shooting either LRGB (with maybe some Ha) or One Shot Colour (DSLR) for galaxies. Yes, you probably are looking at a triplet at the FL needed but it quickly starts to get expensive. However, refractors are regarded as more 'works out of the box'.

The 2 common pieces of advice for astroimagery appear to be:

1. Read 'Makin every photon count', which I'm going to read a second time.

2. It can get expensive!

[Sp@ce_d]

The 2 common pieces of advice for astroimagery appear to be:

1. Read 'Makin every photon count', which I'm going to read a second time.

2. It can WILL  get expensive!

[ollypenrice]

Galaxies, apart from a few, need focal length. You can consider using a shorter focal length and smaller pixels, I suppose.

Trouble is, long focal lengths/high pixel resolution require pecision guiding. This won't come out of a box. It is much easier to start with a short focal length, really. If you did so you could spend a very long time enjoying M51, M33, and M101. Any one those is worth fifty hours of imaging time. (Actually I do mean it! I worked on an M31 collaboration with over fifty hours of data.)

I'm with Steve and Sara. I'd look at the specific scope, not the generic type. Sara was lucky to find a Pentax but a TV85 should come up fairly frequently. With the TV flattener I'd be happy with that. Most of my scopes are bought second hand. Takahashi FSQ106N for around £2K. (Cosmetically fair, otherwise bang on.) TEC140 for under £3.8K. (Literally as new.)

As Steve says, there is something about that ED80 lens... 

Olly

[Tim]

Trouble is, long focal lengths/high pixel resolution require precision guiding. This won't come out of a box. 

It does if you buy the right box Olly  

@keybaud, can you post some links to the kind of images you would like to capture yourself to give us an idea of what you are hoping for?

A way to make astroimaging even more expensive (if that is possible), is to buy the wrong things early on, and end up having to replace or upgrade them to do what you really want.

Honestly, if I was in your shoes, and if I knew that I was likely to get carried away with the hobby, and looking to take pics of galaxies with a DSLR (which is not a bad option as it goes), I'd be thinking EQ6 + MN190 + ED80 guidescope+ lodestar guidecam.

Or step up to a C9.25 edgeHD with 0.7 reducer and an Off Axis Guider (yum!)

If you want nice pics of galaxies with some detail, then look at scopes around 1000mm or more in focal length. The MN190 is as near to a decent 6" triplet as you will get at around 1/5 of the price. (i've used both!) It has great colour correction, and an almost perfect flatfield, just right for DSLRs, and at f5.3 it is no slouch. If you step up to a CCD, the MN190 is quality enough to warrant the expense.

Of course then you have to learn to collimate, and to guide and so on, but in the words of the curly haired oaf Jeremy Clarkson, "How hard can it be?"  

When I first started out, I was adamant that my budget was £1500 I think, the original post should still be here somewhere......but then I got carried away

If you are able, try and attend one of the star parties and see what folk are using, and the results they get.

Just a couple of ramblings on a wet n windy afternoon  

Tim

[keybaud]

It does if you buy the right box Olly

@keybaud, can you post some links to the kind of images you would like to capture yourself to give us an idea of what you are hoping for?

A way to make astroimaging even more expensive (if that is possible), is to buy the wrong things early on, and end up having to replace or upgrade them to do what you really want.

Honestly, if I was in your shoes, and if I knew that I was likely to get carried away with the hobby, and looking to take pics of galaxies with a DSLR (which is not a bad option as it goes), I'd be thinking EQ6 + MN190 + ED80 guidescope+ lodestar guidecam.

Or step up to a C9.25 edgeHD with 0.7 reducer and an Off Axis Guider (yum!)

If you want nice pics of galaxies with some detail, then look at scopes around 1000mm or more in focal length. The MN190 is as near to a decent 6" triplet as you will get at around 1/5 of the price. (i've used both!) It has great colour correction, and an almost perfect flatfield, just right for DSLRs, and at f5.3 it is no slouch. If you step up to a CCD, the MN190 is quality enough to warrant the expense.

Of course then you have to learn to collimate, and to guide and so on, but in the words of the curly haired oaf Jeremy Clarkson, "How hard can it be?"  

When I first started out, I was adamant that my budget was £1500 I think, the original post should still be here somewhere......but then I got carried away

If you are able, try and attend one of the star parties and see what folk are using, and the results they get.

Just a couple of ramblings on a wet n windy afternoon  

Tim

Thank for the reply. If I'm totally honest, I don't know what I will end up shooting, but I do like pictures of galaxies, such as M31 Andromeda. I am going to spend the next few months looking at my options and doing a lot of background reading, because that is what I'm like! (It's also why my wife refuses to buy me any presents, as she knows that it will be the wrong one for some tiny piece of detail she wasn't even aware of). Having said this, I am also aware that sometimes just getting something may be better than 'analysis paralysis', but there is a lot of information out there and I'm enjoying the research so far.

Factors I consider:

I am unlikely to buy a CCD camera (at least in the near future), as I don't have the funds, so the photos will be with a DSLR.

I may not be able to afford everything at the start, so I want to get the items in the order my son and I will get the most out of.

I could use my son's 70mm travelscope as the guidescope on the first telescope I get.

Your post has now made me wonder whether I reconsider an 80mm as the first scope and get the MN190 (I just saw some of the galaxy photos on Google!!!) and a EQ6. I can use this for viewing with my son until I get the rest of the AP act together and I could practise guiding with the 70mm.

[keybaud]

Your post has now made me wonder whether I reconsider an 80mm as the first scope and get the MN190 (I just saw some of the galaxy photos on Google!!!) and a EQ6. I can use this for viewing with my son until I get the rest of the AP act together and I could practise guiding with the 70mm.

Oooooooh, and FLO do the pair as a bundle...

[nleitao]

On 23/12/2013 at 18:06, keybaud said:

It's also why my wife refuses to buy me any presents, as she knows that it will be the wrong one for some tiny piece of detail she wasn't even aware of.

How I understand you!

[alacant]

On 21/12/2013 at 18:07, keybaud said:

micro-analysing things

Hi

There's no way I could decide either.

The best way by far when trying to make a decision one way or another is to make a shortlist and take it along to your local astro club. Nothing can compare with hands on experience.

Try to keep an open mind though as everyone you'll speak to at astro clubs has the best telescope;)

Cheers and HTH

Edited May 8, 2020 by alacant