Test and Comparison: Starfield 102mm F7 ED Doublet v Takahashi FC-100 DF f7.4 Doublet (Fluorite)

[jetstream]

Just now, 900SL said:

Would it be correct to say that this is more a visual astronomy thing? 

With respect to imaging, I thinks its more of "perfect data in, perfect data out" deal,  figuratively speaking.

[paulastro]

'Empty Magnification' used to be the expression  used to descibe using magnifications so high that the image deteriorated to such a degree that the image became unusable.

While a 100mm fluorite doublet refractor still being sharp on planets at x500 plus is impressive, it doesn't mean it is necessarily a good image.  That depends on  the observer according to their age, experience, observing skill and what they perceive as being a good image.  Everyone will have a different opinion.

I'm a very experienced observer, and by no means the worst or best, and also fast approaching  68 years old. And, aging in all of us affects what we see.

To me a 100mm doublet fluorite image on any planet at much over x250, though still sharp, will be very pale, fairly colourless and being bombarded by numerous floaters.  A good example of 'empty magnification'.

At x250 in my 8inch Dob the image will be as sharp (when the seeing allows), much brighter, far better saturated colours and floater-free.  A good example of 'useful magnification'.

 

 

[neil phillips]

2 hours ago, Mr Spock said:

There could be a definition of sharp should you choose to accept the laws of optics/physics. However, people prefer their own definition of sharp. As such it is impossible to know what people mean when they say sharp as only they can see what they are looking at and give their interpretation of what they see.

For this test at just below x300 I would describe both scopes as reasonably sharp and usable rather than bitingly sharp. Some will make excuses like it was the seeing etc. That's why I had the 12" Dob there too as it is a large aperture Newt which is susceptible to poor seeing. It was not. Compared to the two fracs at the same magnification it was bitingly¹ sharp, detailed and full of contrast, and by direct comparison both fracs looked soft - dialing back the magnification to x150 in the fracs gave a sharp image equivalent to the x300 of the 12"; more or less what the laws of optics tell you it should under ideal conditions. 4" is 4" regardless of the quality of the optics.

As I said, only the observer knows what they are seeing.

¹ We must be careful about using subjective terms as they too are open to interpretation 

Couldn't agree more and this is also what I've seen when I image. Less subjective. Same observation

[Greymouser]

I cannot comment on any Tak, I have never used one, probably never will. I did however have the Starfield side by side with the Bresser F 13.2, same aperture. I have always struggled judging which label to put on seeing, etc. but on that night I would have said above average and my target was mainly Lunar, with some other wandering. I felt that the Starfield was losing sharpness above 200x whatever that means. The Bresser was better, more detailed, sharper and far more pleasing. Also still great well past 300x. Of course, this could be just me. 

I also found the Bresser 102 to be better than the Bresser 127L, again side by side. Just more pleasing. 

I am still considering another Starfield, with another lightweight mount. 

[Greymouser]

2 hours ago, Mr Spock said:

We must be careful about using subjective terms as they too are open to interpretation 

So very true about so much, not just astro related.

[mikeDnight]

*

Edited April 5, 2023 by mikeDnight

[Ags]

2 hours ago, Mr Spock said:

There could be a definition of sharp should you choose to accept the laws of optics/physics

The laws of physics were developed centuries before Takahashi made their first telescopes, so they clearly don’t apply 🙂

[Paz]

I agree with comments above that good eyesight matters when getting the most out of a small high end refractor at high magnifications, and so does experience, technique, and the conditions.

The laws of diminishing returns apply but although the gains are marginal and despite me being very happy with my altair 102mm f7, a 100mm Tak remains on my hit list, not right now but eventually.

The reason why is the same as why I have T/&×@*e eyepieces  (name redacted to avoid further controversy!). I know other  lower cost items are very close (and in the real world of the wobbly stack they are just as good really) and unless you A-B them side by side or are very experienced, it can be tough to spot the difference but I enjoy my observing more because I believe I can't get anything better and so it is all down to me and my ability to get the best out of them. This means I'm totally focused on enjoying observing and I'm not thinking about what other kit I might use.

Edited March 31, 2023 by Paz
Typo

[John]

3 minutes ago, Paz said:

.....I believe I can't get anything better and so it is all down to me and my ability to get the best out of them. This means I'm totally focused on enjoying observing and I'm not thinking about what other kit I might use.

I think that is a good objective to have. Get the best that one can and then practice, practice, practice to get the very best out of it that the conditions and other "wobbly stack" factors will allow.

It is quite satisfying to think, sometimes, that the view one is getting is likely to be as good as any equipment can give within the constraints of the aperture, observing conditions and ones own ability. 

[F15Rules]

1 hour ago, paulastro said:

To me a 100mm doublet fluorite image on any planet at much over x250, though still sharp, will be very pale, fairly colourless and being bombarded by numerous floaters.  A good example of 'empty magnification'.

At x250 in my 8inch Dob the image will be as sharp (when the seeing allows), much brighter, far better saturated colours and floater-free.  A good example of 'useful magnification'.

That's a great summary, Paul..

The first paragraph I can totally identify with, even almost to the age (I'm 67)..

I have found that binoviewing really helps reduce the visibility of floaters at higher powers, and in my FS128 on good, steady nights I can get to 300-350x on Lunar, doubles, globular clusters and Mars/Saturn with comfortable and rewarding views. On more normal nights for my location, ( we have a local micro climate due to surrounding low hills creating temperature inversions, especially in earlier evenings) and with Cyclops viewing, it would be more like half that, and in the case of Jupiter it's rare for me to be able to go much above 150x.

Regarding your second paragraph, I can totally accept and respect that that is your experience. For myself, I just don't like reflectors, never have. I find them uncomfortable to view through, ugly to look at and fiddly to maintain. I'd be the first to admit that I didn't persevere with them, as I knew early on that they would never float my boat.

I just prefer the look, comfort and low maintenance of refractors, both apo and long achromat. I accept that a good, larger reflector may well show more, and on occasion significantly so, but my refractors will deliver more of the sharp, high contrast views that I want, more often, on the relatively few clear nights we get in the UK.

If I couldn't have a refractor I'd have a good Maksutov which IMHO can give the most refractor like views of any of the other types of telescope 😊.

Dave

 

[paulastro]

1 hour ago, F15Rules said:

That's a great summary, Paul..

The first paragraph I can totally identify with, even almost to the age (I'm 67)..

I have found that binoviewing really helps reduce the visibility of floaters at higher powers, and in my FS128 on good, steady nights I can get to 300-350x on Lunar, doubles, globular clusters and Mars/Saturn with comfortable and rewarding views. On more normal nights for my location, ( we have a local micro climate due to surrounding low hills creating temperature inversions, especially in earlier evenings) and with Cyclops viewing, it would be more like half that, and in the case of Jupiter it's rare for me to be able to go much above 150x.

Regarding your second paragraph, I can totally accept and respect that that is your experience. For myself, I just don't like reflectors, never have. I find them uncomfortable to view through, ugly to look at and fiddly to maintain. I'd be the first to admit that I didn't persevere with them, as I knew early on that they would never float my boat.

I just prefer the look, comfort and low maintenance of refractors, both apo and long achromat. I accept that a good, larger reflector may well show more, and on occasion significantly so, but my refractors will deliver more of the sharp, high contrast views that I want, more often, on the relatively few clear nights we get in the UK.

If I couldn't have a refractor I'd have a good Maksutov which IMHO can give the most refractor like views of any of the other types of telescope 😊.

Dave

 

Many thanks Dave.

I actually use a binoviewer, barlow and Orthos for virtually all my lunar and planetary observing, and they do make a huge difference. Usually this is x200, and sometimes up to around x300 or so, more for Mars.

I accept liking to use some scopes above others is a good reason to use them.  I like using refractors and reflectors the most, with a slight preferance for the latter as I really don't like seeing mirror images in diagonals. It just bugs me as it's not a 'real' view which you can actually see if you get in a rocket and travel out into space!

My 8 inch is used for nearly all my obs because, for me,  it shows more detail in planetary and deep sky than my 80mm ED.  In fact, I sold my Tecnosky 102ED version of the Starfield to pay for my dob.  It was just as excellent as the Starfield but I wanted the extra aperture to allow me to see brighter images of planets at the mags I needed to use and more detail in deep sky.  This it does very well and I don't miss the Tecnosky to be honest.

Another reason I bought it was it is the Celestron 8inch Starsense Explorer Dob.  It has been a real game changer in terms of finding objects quickly and without using a finder.  I have severe hip  and back problems and sat down observing with the help of pain killers I'm enjoying my observing as much as I ever have.

So in the end, I just have the best scope that suits me personally in both what I want to see, and that I can physically cope with at the present time.

Whatever scopes I have in the future, I will have to mod them to use the Starsense Explorer system. 🙂.

[F15Rules]

You have clearly chosen exactly the ideal setup for your needs Paul👍.

I've no idea how the Starsense system works, but it sounds as though it really saves you time and effort in locating targets, and that has to be a good thing!😊

Dave

[paulastro]

Thank you David.  

If I start writing about the Starsense Explorer I'll be up until the early hours 😊.

There us a good review by Alan Dyer below

https://astrogeartoday.com/celestrons-new-starsense-dobsonians-reviewed/

Also an excellent review by Ade Ashford in September 2022's Astronomy Now.

I've also put a review on SGL somewhere but I haven't got a link for it.

There's a very good review on the SS dob by High Point Scientific on u-tube .  

Lots of info on SGL too.

Well, you did ask  David 😅

 

Edited March 31, 2023 by paulastro

[bosun21]

Another thumbs up for the Starsense unit. I swap mine between my 12” dobsonian and my Starfield 102. This being my second Starfield as I foolishly sold my first one. I found that I missed owning and using a good quality frac. As much as I love both my telescopes I would be lying if I didn’t admit to having one crafty eye on a shiny new Takahashi 🔭👁.

[John]

Looking at the comparative prices of these instruments, the Takahashi is 3 times the price of the Starfield 102. 

I don't know how much effort goes into the manufacture of these scopes but currently the average wage in Japan, where the Takahashi is made, is about 4 times as much as it is in China, where the Starfield is made. 

Such a difference is bound to impact the retail cost of these products and their comparative quality, with the advantage being strongly towards the Chinese product I would think ?

NB: this is not in any way intended to be a political comment, it is merely factual (based on current data) which, IMHO, is likely to have a material impact on the relative costs of these telescopes.

 

 

[jetstream]

22 minutes ago, John said:

I don't know how much effort goes into the manufacture of these scopes

Rumour around the campfire is the Chinese optics are well figured, but possibly rushed a bit in the polishing process, affecting smoothness potentially. Opticians will slowly take the optic to a point where improvements either stop or go backwards. If it inadvertently goes far enough backwards they have to start all over. I'm not so sure they ^^ do that- or just release it if it meets their minimum standard whatever that is. IMHO.

[John]

21 minutes ago, jetstream said:

Rumour around the campfire is .......

It's good to know that the Chinese manufacturers join in these "campfire" chats and reveal their secrets 🙂

[bosun21]

Do any of you proud Takahashi owners actually sleep?😂

[Sunshine]

On 30/03/2023 at 12:54, jetstream said:

spacial frequency and angular resolution.

These thoughts could not be further from my mind when I'm looking at the moon through either of my telescopes, sorry Gerry.

[JeremyS]

7 hours ago, John said:

Looking at the comparative prices of these instruments, the Takahashi is 3 times the price of the Starfield 102. 

I don't know how much effort goes into the manufacture of these scopes but currently the average wage in Japan, where the Takahashi is made, is about 4 times as much as it is in China, where the Starfield is made. 

Such a difference is bound to impact the retail cost of these products and their comparative quality, with the advantage being strongly towards the Chinese product I would think ?

NB: this is not in any way intended to be a political comment, it is merely factual (based on current data) which, IMHO, is likely to have a material impact on the relative costs of these telescopes.

 

 

Will have a large effect on cost of manufacturing those lovely Tak focusers which are hand cast and hand finished 👍🏻😊

[paulastro]

6 hours ago, jetstream said:

Rumour around the campfire is the Chinese optics are well figured, but possibly rushed a bit in the polishing process, affecting smoothness potentially. Opticians will slowly take the optic to a point where improvements either stop or go backwards. If it inadvertently goes far enough backwards they have to start all over. I'm not so sure they ^^ do that- or just release it if it meets their minimum standard whatever that is. IMHO.

That 'rumour' wouldn't come from another forum over the pond would it?  Do you actuuually know the source?The trouble with rumours is that the more they are passed on, the more they become accepted as being true - and they can cause serious damage to people's reputations and livelihoods.

Personally, I'd doubt this to be true.  The Starfield and the other badged examples are so good I'd have thought it unlikely.  Anyway, with the cost of labour in China, there is no reason for them to 'rush a bit''.

Though, there's nothing wrong with having minimum standards as long as they are high enough, I presume every manufacturer of optics have to have minimum standards.  I've not heard of a bad example of the Starfield or the other versions myself.

[Moonlit Knight]

Many thanks for posting, in someways a brave thing to do, so thank you again, much appreciated. In response to your excellent comparison your results are pretty much as most of us suspected I would imagine. They (TS/Altair/Technosky/Starfield) are just good scopes. Those of you who have owned horses will know what we mean when I suggest they are honest, they really are very honest telescopes and a very safe telescope to purchase. There are no nasty surprises, everything just works and is compatible with the the rest of the astronomy world. 
 

Anyway whatever you decide to use just use and enjoy it.

Clear skies to you all. 
 

 

[Moonlit Knight]

14 hours ago, paulastro said:

'Empty Magnification' used to be the expression  used to descibe using magnifications so high that the image deteriorated to such a degree that the image became unusable.

While a 100mm fluorite doublet refractor still being sharp on planets at x500 plus is impressive, it doesn't mean it is necessarily a good image.  That depends on  the observer according to their age, experience, observing skill and what they perceive as being a good image.  Everyone will have a different opinion.

I'm a very experienced observer, and by no means the worst or best, and also fast approaching  68 years old. And, aging in all of us affects what we see.

To me a 100mm doublet fluorite image on any planet at much over x250, though still sharp, will be very pale, fairly colourless and being bombarded by numerous floaters.  A good example of 'empty magnification'.

At x250 in my 8inch Dob the image will be as sharp (when the seeing allows), much brighter, far better saturated colours and floater-free.  A good example of 'useful magnification'.

 

 

What he said…

If I go above  x 150 the floaters start to take over and ruin the view, so there’s little point really. 
 

[Moonlit Knight]

7 hours ago, jetstream said:

Rumour around the campfire is the Chinese optics are well figured, but possibly rushed a bit in the polishing process, affecting smoothness potentially. Opticians will slowly take the optic to a point where improvements either stop or go backwards. If it inadvertently goes far enough backwards they have to start all over. I'm not so sure they ^^ do that- or just release it if it meets their minimum standard whatever that is. IMHO.

Rumour is confirmation bias is rampant on astronomy forums, and just about everywhere else. We ALL choose to believe what we want to believe 

[Alan White]

Can I just check with Starfield owners…..

Are your scopes China made or Taiwan made? I think the latter.

Not a political point, more a are we all making correct comments folks?