Review: Saxon 70mm f/7 Achromatic Refractor

[iceman (Mike)]

Hi all.

Chris Lewis has written a review of the Saxon 70mm f/7 Achromatic Refractor.

You can read the review on the IceInSpace Reviews page or directly by clicking the link below:

Saxon 70mm f/7 Achromatic Refractor

Thanks to Chris for writing the review! If you'd like to submit a review, article or anything else for IceInSpace, please Contact Me.

[iceman (Mike)]

Review uploaded.

[allan gould]

Might add that I purchased this scope as a light guidescope for my 8" and find that it easily holds focus without slippage. Was cheap to buy as an OTA at about $150 and works well.

[ballaratdragons (Ken)]

Originally Posted by allan gould

Might add that I purchased this scope as a light guidescope for my 8" and find that it easily holds focus without slippage. Was cheap to buy as an OTA at about $150 and works well.

Allan, where did you find this scope for $150?
Best price I can find by googling is $349 but that also includes Tripod. Be nice to find just the OTA for $150.

This could be the type of scope David & Barb are after for guiding

[Tamtarn]

Thanks for thinking of us Ken and posting on this thread.

As a matter of fact Allan must have seen our other thread that same night and had contacted us about the Saxon as a guidescope just before you posted here.

He offered us his Saxon scope and we just had to wait until he checked if a DSI Pro would come to focus as he had modded the scope and we have a DSI Pro on order.

He confirmed yesterday that it was OK so we should have the scope sometime next week.

WOO HOO !! Autoguiding

Just have to wait for the DSI now. Can't wait to see your imaging with the DSI when you get it up and running ................ Hope your old Toucam holds out until then

[ballaratdragons (Ken)]

Originally Posted by Tamtarn

He confirmed yesterday that it was OK so we should have the scope sometime next week.

WOO HOO !! Autoguiding

It's actually fun watching it Autoguide

Geez, we are like big kids

Originally Posted by Tamtarn

Hope your old Toucam holds out until then

So do I, but only 2 sleeps to go and it should be here

Before I post anything with the DSI, I want to do a 'last image' with the Toucam. For old times sake

[Barnacle (Bill)]

Hi All,

I got a used 70mm f500 of this telescope with its mount and I love the quality of the objective lens of this scope from Synta!

On close inspection, there is a welded baffle mid-way in the main scope tube, closer to the objective lens end and another baffle ring inside the middle of the focuser draw tube.

Together, they stopped down the effective aperture to 60mm, from the lens diameter 70mm. I removed the plastic baffle ring inside the focuser draw tube, by breaking it into bits (made of white plastic painted black) using a hammer and a screwdriver. That takes the effective aperture to a max of 62mm. The scope aluminium tube diameter is about 80mm, less than its 70mm f900 cousin.

The question I need help on is how to reach and cut and enlarge the welded aluminium or metal baffle ring inside the main scope tube?

The baffle can’t be hammered out or moved along the scope tube, as it is welded into place.

The plastic objective cell is glued/moulded into place. One can unscrew the plastic objective lens retainer ring and take the doublet lens and plastic spacer out (which I did to clean the lens on my unit as it was quite dirty when I got my used unit), but the plastic lens cell, connected to the aluminium main scope tube can’t be removed, as it’s glued/moulded into place.

I also don’t want to remove the baffle totally, but like to enlarge the diameter of this baffle instead, so that the scope uses its full 70mm aperture, and to use this baffle as it should be designed for, ie, cutting out stray light and not as an objective lens diameter restrictor.

The objective lens on my unit, which I star tested on Sirius is great (the doublet lens were marked on their lens edge, so you can put it back in collimated and aligned), I just wish it wasn’t stopped down to 60mm.

Thanks.

Bill

[raymo]

The baffles in refractors don't stop down the scopes, except in the case of very low quality finders, and department store scopes that are little more than toys. My 102mm has two baffles, and the one near the middle of the tube is about 65mm diam. The light cone is down to that size by the time it reaches the baffle. The same goes for my 80mm, where the mid tube baffle
is about 45-50mm diam.
raymo

[MattT]

Hi Bill,
I had one of these refractors for a number of years and it gave great views.

What makes you think it stops the aperture down? Never thought mine did. Looking through the focuser end without an eyepiece in I could see the 3 spacer tabs on the objective. I gave the scope away in the end as I wanted a small scope with a 2" focuser...an expensive exercise

Matt

[Barnacle (Bill)]

Hi raymo and Chris,

Many thanks both for your replies.

http://www.cloudynights.com/topic/43.../#entry5566084

I did the above "flashlight" test on this 70mm unit and it gave a 60mm image when measured with the ruler. I use this test for my binocs also, and the current Chinese binos are usually stopped down compared to the 1960s Japanese ones. They just don't make things like they used to, scopes or binocs.

I tested the same with my 60mm frac after I knocked out the baffle inside the draw tube (it also had a baffle ring inside the draw tube)and it then showed a 60mm image with the 3 spacer tab visible in the image. Before the focuser drawtube baffle was knocked out, the image was only 50mm and I couldn't see the spacer tabs. The baffle on the main tube of the 60mm did not act as aperture stop on this occasion, and it is a 60mm f700 Tasco, but the baffle ring in the focuser certainly did.

Using the test, I am pretty sure the baffle on this 70mm f500 unit acted more than being a baffle but an aperture stopper or diameter restrictor from 70mm to 60mm as well. As such, I like to reduce the baffle in the main tube, not to remove it, just thinking what is the easiest way to go about this?

I agree, in good quality scope, the baffle should not act as aperture stop, but this unit does. After all, this 70mm 500mm is not that far from dept store as it is mass produced under different brand names from Synta.

PS: Don't get me wrong, it also gives great views but it would do better as a true 70mm than stopped down 60mm I think.

Thanks again both for your replies.

Bill

[MattT]

Hi Bill,

Welded you say....I'd give a few gentle taps with a thick bit of wood and a hammer and see if it moves. Might be spot glued rather than welded. You might be able to knock it down the tube to where it doesn't cut the aperture down and glue it there yourself? The objective on mine was screwed on and the whole cell came off.

Good luck.

Matt

[Barnacle (Bill)]

Hi Matt,

Many thanks for your reply and will gladly accept your wish me luck here.

Will find a thick pole or stump and give it a big whack or two to see if I can nudge this baffle further down the tube and not tilt it or bend it... If it does move, I think this baffle will be pretty fixed and won't move around without adding any glue, whatever i can move it further down the tube.

If that doesn't work, if the baffle is aluminium and thin enough, I am thinking of using a utility knife, extend the blade and reach it (after all it is closer to the objective end) by cutting small 1 cm incisions all along the inner perimeter of that baffle ring and then fold it back bit by bit to enlarge the opening if I can reach it and fold it back with a plier or something. Then repaint the then enlarged and less than perfect circle in black for any shiny cut of raw metal due to my DIY.

Waste of aperture from 70mm to 60mm as it is at the moment as light gathering power is quintessential for astronomy, which I am using it for.

I can take the objective lens out after unscrewing the retainer ring, and the doublet is spaced by a plastic ring, not spacer tabs, but it is a real good quality doublet lens on my used unit (after I cleaned the real filthy objective lens both end when I first got it). I was real impressed to see the arrow marked at the edges of the Crown and Flint glass lens, so you know exactly where they should match each other when put back together for alignment and collimation.

That much I established with this unit's doublet lens when I star tested it on Sirius, hope it will stay this way when I enlarge it to its full 70mm aperture. The same with my Synta 70mm f900 frac, the objectives on that frac is also real nice.

I agree with you, this little scope (at the moment) gives great views, and in mine it is violet free on the Moon's limb with 6.5mm + 2x barlow (153x), despite at f7.1, to my surprise!

I don't think my Synta 70mm f900 was that violet free on the Moon's limb, need to try it later on to compare at around the same power.

Thanks heaps again for your quick reply, much appreciated.

Bill

[raymo]

I am really surprised that your baffle stops the scope down. The
manufacturer would never do that unless the lens displays aberrations at
full aperture, which is, of course, exactly what el cheapo lenses do. Most
refractors have a baffle in the draw tube, it acts as a field stop, like the
ones in eyepieces.
Not surprising that the violet fringe is much reduced, the 2x barlow makes
your scope f/14.2.
raymo

[Barnacle (Bill)]

Hi Raymo,

Many thanks for your latest reply.

I hope to find out whether the doublet lens is el cheapo or they just baffle them anyway as they are mass produced by Synta under different brand names this 70mm f500 unit. Stopping a 70mm to 60mm certainly helps to remove the lens aberration where it is greatest at the edge and improve the visual quality of the image.

As for the barlow effect, good point you raised. I add that I observed the Moon alone with the 6.5mm eyepiece on its own and it was still violet free, so happy with this 70mm or stopped to 60mm unit.

My other Synta 70mm f900 frac, there is a stopper ring in the draw tube, but it is tiny, a mere 1-2mm indentation (unlike this short tube, where the draw tube baffle ring is a good 7-8mm). I haven't done a flashlight test to see whether the 70mm f900 is also stopped down.

I only got curious about stopped down lens recently when first comparing binocs of yester years from Zeiss, UK and from Japan with the binocs pumping out of China now, and extended to small fracs, eg, Tasco 60mm frac.

I also got piqued experimenting with those "toy" 50mm single glass (non-doublet) positive meniscus lens refractor scopes from Tele-Science. Tele-science sells a 50mm f10 and a 50mm f14, and both are single positive meniscus lens refractor scopes and how they are stopped down both with one main tube baffle and 2 draw tube baffle rings to achieve a clean and sharp image, with effective real aperture down from 50mm to 30mm instead with all the 3 baffles in place when I did the flash light test on them.

I will never forget the experience of looking at Orion nebula with the Tele-science 50mm f10, and how I saw a very dark sky, despite I was near Melbourne city with light pollution, with the trapezium stars pin point sharp, but Orion nebula was no where to be seen in the dark background. The three baffles were so effective in cutting out all the light and reduced the aperture of this 50mm f10 scope, that Orion nebula disappeared altogether. It was an experience to behold in "baffle" astronomy. Yet with the 50mm f14, with the 3 baffles in place, Orion nebula is still clearly visible, despite both Tele-science scopes were stopped down from 50mm to 30mm and both have 3 baffles in place.

I also got fascinated at how the plastic lens eyepieces from Tele-Science deliver a more contrasty and less wash out image than my 3 element glass Kellner or 2 element Huygens/Ramsden eyepieces.

Back to topic, the short distance of this baffle from the objective on this 70mm short tube scope got me suspicious on first inspection, esp the size of the baffle opening and the flash light test confirmed that it was stopped down to 60mm.

PS:
Will keep you and Matt posted if I managed to enlarge the baffle and restore this unit back to 70mm and whether the lens is el cheapo, ie, image degrades and colour galore, I certainly hope not.

Many thanks.

Bill

[brian nordstrom (As avatar)]

Thanks for this excellent review Chris , these scopes seem to get forgotten today in our world of Tak this , APO that , AP only , CA bad ! ,, etc. etc. etc .

I have a slightly larger version , a 90mm f10 Saxon that I grabbed here and now mounted on my Vixen Super Polaris mount it has become my favorite grab and go scope , enough aperture and quality of the lense cell , figure , coatings and focuser to give really good views of the moon and planets , deep sky aint bad either , it performs wonderfully on Jupiter and I am hard pressed to see any CA even at 170x ( I have taken it to 220x ) it has nice optics and the quality Vixen mount helps .

On the stopping down I checked that as soon as I got this OTA and it is performing at the full 90mm but the focuser ,, woaw !!!! , the focuer was that far out of allignment that the laser collumator's beam did not even touch the lense , terribly out .

the screw holes were found to be about 3mm out in one direction , terrible QA , but an easy fix if you know its there , not so for a newby very , very sad really and like this the views fell apart at 80x with this mis-allignment .

But it now is a good performer and thanks again for your time in putting this review together . .

Brian.

[MattT]

Hi Bill,
Good to know your another long fl achro fan....like Brian and myself

I too have the 70x900 which I really like and rides as a finder scope on my 6" f12 refractor.

I'm not surprised at the badly placed...or intentionally perhaps...baffle. heard of it many times with ST scopes.

To complete my long achros I have a 6TE...50mm f12 Tasco which is a real cuttie.

I like your idea of cutting the baffle and sticking a proper sized baffle on it.

Please post your results.

Matt

Ohh I forgot....90x1000 Achro from the mid 90's....great scope...so good I kept it and sold an ED 100 f9.

[Barnacle (Bill)]

Hi Matt,

Yes, I love fracs, and Chris Lewis' review on this cheaper and versatile frac has a very important role. I am not an expensive taste amateur, believing in 90% can be obtained from modest scopes, leaving the next 10% to expensive scopes. Astronomy can be accessible to most on very modest budgets with decent brands catered for mass produced scopes, and Saxon, Bresser and Skywatcher are good brands with their achro fracs.

I only venture out recently to reflectors and now trying short(er) tube fracs recently. Reason is I have one of those little 50mm f360mm (f7.1) Chinese refractor scopes with 0.965 focuser and 90 degree diagonals as a finderscope, replacing my original straight thru 50mm finder scope.

It is a real pain to use a straight thru finder when you are pointing up the zenith. I was quite happy with the quality of f7.2 on these 50mm fracs, ie, f7 is versatile as a grab and go and wide field short(er) tube scope. That's why I picked up this 70mm f500 to try it out.

Agree wholeheartedly, very common or the norm to stop down short tube frac so they deliver better images. In my case, by stopping 70mm to 60mm on my unit by the maker, it is no longer f7.1 but f8.3 and using better part of a lens margin in a 70mm as opposed to the edge of a 60mm to form an image, as such, it should deliver nice images. The Q is what happens if we open up and let it be a full 70mm instead? Time will tell, will keep you and raymo posted if I managed to get to that baffle with my basic tools.

I have a Tasco 60mm f15 scope, but it is a dud at the moment, the doublet lens needs to be rotated to find the sweet spot as it is badly out of alignment when I got it, QA is not a necessity or a must with mass produced units out of China.

Wow, you have 6 inch f12! The crispness and sharpness and lack of violet must be fantastic on a f12. Yes, I love my 70mm x f900, the Airy disks on stars and splitting double stars is a joy on this little long frac. Long achro fracs has its place with some of us, as much people move onto the modern bg $$$ frac cousins such as Apo, ED, fluorite etc.

The old Crown and Flint doublet design in fracs and long f ratios will last a long time if well care for. We have our 40 inch Yerkes and 36 inch Licks doublet fracs as testament to their durability and purpose. Extract below is a reminder of the old doublet frac versus the new modern fracs:


http://www.jayreynoldsfreeman.com/Au...s/GBU.text.pdf

They were comparing high end 5 inch modern Tak, Meade ED, AP refractors on various objects including Jupiter, then trained the 36 inch Lick Observatory doublet frac on Jupiter as a comparison:

There is one final bottom line: 3.) APERTURE WINS. Remember, this test was conducted at Lick observatory. At the end of the evening, we all went inside and had a look at Jupiter through the 36-inch refractor. This instrument was loafing -- its 55 mm Plossl eyepiece delivered 316x and an exit pupil nearly 3 mm in diameter -- one we associate more commonly with looking at galaxies and emission nebulae than at planets. Even at f/19, a three-foot conventional doublet has a lot of secondary color, and although the seeing was very good, it was not perfect for such a large instrument. Nevertheless, the 36-inch blew us all away. Features only hinted at in our puny five-inch instruments were shown clearly and with lots of detail in the big refractor. How humbling, to be reminded that the best of our modern, high-tech, high-end instruments was barely qualified to replace the finder on this century-old leviathan.

Thanks again, you must be real proud of your f12 yard cannon, must be a real joy to own such a large, fine precision scientific refractor instrument.

Kind regards,

Bill

[Barnacle (Bill)]

Hi Matt,

Yes, I love fracs, and Chris Lewis' review on this cheaper and versatile frac has a very important role. I am not an expensive taste amateur, believing in 90% can be obtained from modest scopes, leaving the next 10% to expensive scopes. Astronomy can be accessible to most on very modest budgets with decent brands catered for mass produced scopes, and Saxon, Bresser and Skywatcher are good brands with their achro fracs.

I only venturing out recently to reflectors and now trying short(er) tube fracs recently. Reason is I have one of those little 50mm f360mm (f7.1) Chinese refractor scopes with 0.965 focuser and 90 degree diagonals as a finderscope, replacing my original straight thru 50mm finder scope.

It is pain to use a straight thru finder when you are pointing up the zenith. I was quite happy with the quality of f7.2 on these 50mm fracs, ie, f7 is versatile as a grab and go and wide field short(er) tube scope. That's why I picked up this 70mm f500 to try it out.

Agree wholeheartedly, very common or the norm to stop down short tube frac so they deliver better images. In my case, by stopping 70mm to 60mm on my unit by the maker, it is no longer f7.1 but f8.3 and using better part of a lens margin in a 70mm as opposed to the edge of a 60mm to form an image, as such, it should deliver nice images. The Q is what happens if we open up and let it be a full 70mm instead? Time will tell, will keep you and raymo posted if I managed to get to that baffle with my basic tools.

I have a Tasco 60mm f15 scope, but it is a dud at the moment, the doublet lens needs to be rotated to find the sweet spot as it is badly out of alignment when I got it, QA is not a necessity or a must with mass produced units out of China.

Wow, you have 6 inch f12! The crisp and sharpness must be fantastic on a f12. Yes, I love my 70mm x f900, the Airy disks on stars and splitting double stars is a joy on this frac. Long achro fracs has its place with some of us, as much people move onto the modern bg $$$ frac cousins such as Apo, ED, fluorite etc.

The old Crown and Flint doublet design in long f ratios will last a long time if well care for. We have our 40 inch Yerkes and 36 inch Licks doublet fracs as testament to their durability and purpose. Extract below is a reminder of the old doublet frac versus the new fracs:


http://www.jayreynoldsfreeman.com/Au...s/GBU.text.pdf

They were comparing high end 5 inch modern Tak, Meade ED, AP refractors on various objects including Jupiter, then trained the 36 inch Lick Observatory doublet frac on Jupiter as a comparison:

There is one final bottom line: 3.) APERTURE WINS. Remember, this test was conducted at Lick observatory. At the end of the evening, we all went inside and had a look at Jupiter through the 36-inch refractor. This instrument was loafing -- its 55 mm Plossl eyepiece delivered 316x and an exit pupil nearly 3 mm in diameter -- one we associate more commonly with looking at galaxies and emission nebulae than at planets. Even at f/19, a three-foot conventional doublet has a lot of secondary color, and although the seeing was very good, it was not perfect for such a large instrument. Nevertheless, the 36-inch blew us all away. Features only hinted at in our puny five-inch instruments were shown clearly and with lots of detail in the big refractor. How humbling, to be reminded that the best of our modern, high-tech, high-end instruments was barely qualified to replace the finder on this century-old leviathan.

Thanks again, you must be real proud of your f12 yard cannon, must be a real joy to own such a fine precision scientific instrument.

Kind regards,

Bill

[Barnacle (Bill)]

Hi Matt and Raymo,

I removed the objective lens and focuser tonight.

I then nudged the baffle with a pole, it won’t budge. I then managed to hammer the baffle with the same pole and dislodged it from the scope tube. The baffle was not welded nor spot glued.

I then re-inserted the baffle closer to the focuser end, and put the objective lens and focuser back in, then flashlight tested the scope to ensure it is now showing the full 70mm aperture.

Star testing tonight with Sirius does seem to indicate the lens is somewhat out of alignment, as it shows a little astigmatism which it did not before. Maybe I have not placed the objective lens back in properly or the focuser got out of alignment. Astigmatism, as I understand it, should not be correctable by stopping down a scope.

As the Moon is not around at the time of testing, I can’t test the scope for limb colour, but Jupiter is fine at 77x using 6.5mm eyepiece.

I will update more when I experiment with it further with more observations.

Thanks.

Kind regards,

Bill

[Barnacle (Bill)]

Hi Matt and Raymo,

After rotating the objective lens a few times, I am pretty certain the scope suffers a little astigmatism, not really bad, but it is there. It is not as bad as before, but obvious especially as star light hits the outer perimeter of the lens.

By opening to full 70mm, the star image is also is softer than when it was stopped down to 60mm. But overall still a fine and versatile scope, I am happy to leave it open to 70mm as opposed to moving the baffle back up to baffling it down to 60mm.

That's why this scope was deliberately stopped down from 70mm to 60mm, as:
http://toothwalker.org/optics/astigmatism.html

Extract of above:
"A trusty method to mitigate image impairment by astigmatism and field curvature is to stop down the lens."

Live and learn something new every day.

Kind regards,

Bill