Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon EOS dSLR

Reply
 
Thread Tools Search this Thread
Old Mar 12, 2012, 10:22 AM   #1
Junior Member
 
Join Date: Mar 2012
Posts: 5
Default promaster spectrum 7 teleconverter on a EF-S lens?

Hi -

This is my first post to this forum.
(I posted this same question in a different category- reposting to this one as it is seems a better fit.)

I have a startere DSLR - Canon T1i - and my longest lens is a Canon EF-S 55-250 (1:4-5.6).

I recently took a chance at Goodwill and nabbed a Promaster Spectrum 7 2x teleconverter (for Canon EOS 1).

It works fine on my 50mm EF lens and a 28-80 Canon EF lens I have, but I really wanted it to double my longest zoom, which is an EF-S.

Alas, by trying these, I have learned about the difference between EF and EF-S lenses. (red dot vs white square) Grrr

Is there any way to make this Promaster teleconverter fit onto my EF-S lens?

Thanks for your help and advice!

(P.S. This used purchase also included a nice Sigma 28-80 Macro lens... which, sadly, seems to be unable to talk to my T1i... any advice or ideas for that problem? I will post the Sigma lens question in a separate thread, too)
HollyG is offline   Reply With Quote
Sponsored Links
Old Mar 12, 2012, 11:01 AM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,543
Default

One of the things you'll learn about teleconverters is that, not only do they increase the focal length of a lens (in this case, to 110-500mm), they also increase the f-number for the maximum aperture (in this case, to f/8-11.) Since autofocus relies on lenses with maximum apertures of less than f/8, that lens with a 2X teleconverter would never be able to autofocus.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Mar 12, 2012, 11:24 AM   #3
Junior Member
 
Join Date: Mar 2012
Posts: 5
Default no autofocus

Yeah - I had a teleconverter with my old 35mm 10+ years ago. I'm happy to manually focus. My first 35mm SLR was only manual focus! Those were the days

My current problem is just that this converter doesn't physically fit the EF-S lens mount... I'm trying to figure out a work around on a limited budget.
HollyG is offline   Reply With Quote
Old Mar 13, 2012, 2:47 PM   #4
Senior Member
 
WCKSer's Avatar
 
Join Date: Nov 2009
Location: SF Bay Area
Posts: 2,857
Default

I have a Quantaray 2X tele-converter which I bought from Ebay. I think both Promaster and Quantaray are made by Sigma. I did try it on the EF 50 mm F/1.8 and it works but only with manual focus. It works very well with my 24-105 mm f/4 L lens in auto focus mode. However, the Tamron 70-700 mm f/4-5.6 only works in lower range like 70-150 mm in auto and the rest has to go with manual focus. I think the basic requirement for it to work in higher focal length on a zoom lens is to have f-stop F/4 and below. I am not sure if there is a tele-converter out there which is made for the EF-S lens. Even the Canon made tele-converters only work on fixed EF focal lens from 135 mm and up and 70-200mm and up for zoom lens. However, not all Canon made zoom lens are compatible. So you really have to check for compatibility before you buy one.

EF-S lens mount is different from the EF mount because the bottom plastic element sticks out quite a bit, therefore, it will not fit into the tele-converter.
__________________
Canon 5D MKII, EF 24-105mm f/4L, EF 50mm f/1.8, EF 100mm f/2.8L Macro, Tamron 70-300mm f/4.0-5.6 SP Di VC USD XLD, Sigma DG 150-500mm f/5.-6.3 APO HSM.
Canon EOS T3i, 7D and 70D EF 17-40mm f/4L, EF-S 55-250mm f/4-5.6, Sigma 18-250mm f/3.5-6.3 DC OS HSM, 430 EXII Flash.
Sony A200, SLT-A58 System with HVL-F42AM Flash.
Mirrorless APS-C camera: Samsung NX100, Canon EOS-M.
M4/3 systems: Olympus OM-D-E-M5 and Panasonic DMC-G3.
WCKSer is offline   Reply With Quote
Old Mar 13, 2012, 3:20 PM   #5
Senior Member
 
Join Date: Jul 2003
Posts: 3,396
Default

f/8 is Canon's 1d line only, all the other non 1d bodies stop trying to AF around f/5.6.
Discovered that with a EF 100-400mm f/4.5-5.6 L IS lens and a matched Canon 1.4x TC.
The brochure says the two are compatible, but then you get to discover they will work together, but only when manual focusing.

Quote:
Originally Posted by TCav View Post
Since autofocus relies on lenses with maximum apertures of less than f/8
__________________
A smartphone is all the "camera" you really need.
PeterP is offline   Reply With Quote
Old Mar 13, 2012, 3:30 PM   #6
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,543
Default

Quote:
Originally Posted by TCav View Post
... Since autofocus relies on lenses with maximum apertures of less than f/8, ...
Quote:
Originally Posted by PeterP View Post
f/8 is Canon's 1d line only, all the other non 1d bodies stop trying to AF around f/5.6.
Discovered that with a EF 100-400mm f/4.5-5.6 L IS lens and a matched Canon 1.4x TC.
The brochure says the two are compatible, but then you get to discover they will work together, but only when manual focusing.
What I said was less than f/8. Sigma and Tamron superzoom lenses max out at f/6.3, yet they AF on Canon bodies. I've even seen some f/7.1 combinations that worked. It's just that they'll stop working at f/8.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Mar 14, 2012, 8:18 AM   #7
Senior Member
 
deterpawson's Avatar
 
Join Date: Jan 2007
Posts: 393
Default

Hello Holly,
If you GOOGLE or YOU TUBE you will find some very good info on how to convert an EF-S lens to fit the mount, which is probably an EF mount. The rear end of the EF-S mount needs to be shaved off (ouch). Pls note the risk will be on you. If your good at the DIY thingee then go ahead. Otherwise use caution. I personally have not tried it and probably never will. But the info is out there and it can be done.
Good Luck.
Pete.
deterpawson is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 6:01 PM.